DISCLAIMER – In this story I do not own anything except the plot. Harry Potter and its affiliates are the sole property of JK Rowling. The story is mine, the characters aren't.
DISCLAIMER 2 – The characters will be very OOC. So be warned. If you do not like polite Death Eaters or bad Weasleys and things like that, then this story is not for you. I know that many of you enjoy my slash stories, but this story will rarely mention it.
DISCLAIMER 3 – Please note that flaming me because you do not like this story will change nothing. All I will do is laugh at you and move on. HOWEVER, if you abuse my readers, you will earn a one flick of the wand to report abuse and then onto my blocked list. I absolutely, DESPISE someone who insults my readers. You have been warned.
NOTE – I have decided to give this a try. I am not sure how it will come out. So I will update slow as I want to make sure I can complete the story before I start posting to many chapters. I do not want to start and then abandon the story after I get your attention.
PROLOGUE – Harry and his friends find themselves in a whole new world when an enchanted book starts to take key members of Hogwarts and transports them to Atlantis. Harry will find his hands full as he strives to prove to the ancient race of Atlantians that he and his group are worthy to live in the forgotten land. Only those that have the purity of heart will be allowed to enter this forgotten realm. FEATURES: Good Severus. Bad Ron, Ginny, Molly, and Percy. Dumbledore bashing. Takes place after fifth year. Cedric and Sirius are both still alive in this story.
Chapter 1 – A Summer of Changes
Harry was sitting in his room at Number Four Privet Drive. He was sitting with Hedwig working on his summer homework. He would pause every now and then and smile at the snowy owl who had been his friend since he was eleven. He let his mind wander to the last few weeks of the school term. Voldemort had laid a very intricate plan to trap Harry. He had almost succeeded in his plan. It was at the last moment when Lucius Malfoy and Sirius had saved the day.
"Hand over the prophecy," said Lucius smoothly. "If you do, then you and your friends can leave quietly. Force me to take it from you and we will start using wands."
Harry stood there holding the orb that held the prophecy in his hands. He looked around the room. Neville was in the hands of Bellatrix Lestrange. Hermione was in the hands of Walden McNair. Ginny was in the hands of Antonin Dolohov. Ron was at wand point by Alecto Carrow. Luna was bored in the arms of Amycus Carrow.
"Don't give it to him Harry," said Neville. "They will kill us anyway."
Harry looked into the eyes of Lucius Malfoy and almost lost it. Lucius had winked at Harry. It was a dead give away that something was going to happen. Harry lifted his hand and opened it. The orb sat there with the mist swirling in it. As Lucius was about to grab the orb, light appeared and members of the Order of the Phoenix appeared. Lucius grabbed for the orb and "accidentally" knocked it to the ground breaking it.
"Run to Sirius," whispered Lucius. "It is your only chance of survival. This is the only help I can give to you without it appearing that I am helping you."
Soon spells were flying at a rapid pace. It was not long before Harry and Sirius were side by side fending off attacks from the Death Eaters. Harry and Sirius had managed to rescue Hermione. Remus had managed to stun the Carrows and get Luna and Ron to safety. Moody and Tonks were busy fighting with Bellatrix. Neville ran over to Harry and the group all stood there looking around for Ginny. They found her lying on the floor in a pool of blood. She was alive, but she was wounded severely. Minerva, Severus, and Sirius grabbed the teens and ran. Albus appeared and was attempting to capture as many of the Death Eaters as he possibly could. The fleeing group made it to the atrium where they gave pause. Standing before them was none other than Voldemort. Minerva and Sirius threw up the strongest shields they could. Bellatrix ran in shortly after.
"Master," she said. "Dumbledore is here. You have to get out of here. There is something wrong. The Aurors are on their way. We have to get out of here before someone sees you."
Harry replayed the battle between Voldemort and Dumbledore in his mind. Ministry officials appeared and saw with their own eyes that Harry had been telling the truth the whole time and Voldemort really had returned. When the battle between the two most powerful wizards on the planet was finished he came out of his memories. He started talking to Hedwig.
"What doesn't make sense, Hedwig, is why Dumbledore was just waiting," he said out loud. "It was like he was waiting for something else to happen. I mean he didn't even start throwing hexes until Voldemort did. It was as if he wanted something else to happen. I saw his disappointed look when Sirius and I were standing there. What was he after? I would also like to know why Voldemort didn't attempt to do anything to me. It was like his attention was fixed solely on Dumbledore and I was just a spot on the wall."
"I think I know," said a voice at the door.
Harry turned and Sirius and Severus were standing there. He smiled at the two before he got up. Both men wrapped him in a warm embrace.
"How are you Harry?" asked Severus. "Has Petunia and Vernon been treating you better?"
"Yes," said Harry. "Apparently whatever you told them worked. I am not asked to do anything anymore. I also get three substantial meals a day now. I did volunteer to continue to do the yard work. I like working in the garden. It gives me time to think as well as something to do. Aunt Petunia is not complaining as her garden looks better than every other garden on the block. She even thanked me yesterday."
"So what are you doing here?" asked Sirius. "You are sitting here with a smile on your face and you are talking to Hedwig."
"I was just finishing my Potions homework," said Harry. "Professor Snape asked for three feet on the Draught of Living Death. I was talking to Hedwig because she is intelligent and likes for me to share my thoughts with her."
Severus was looking over Harry's homework. He smiled as he put it back down.
"Your work on this piece of homework is very good," said the Potions Master. "You have even given me a foot more than I asked for. It is very well written. At this rate you will pass Draco and Miss Granger in no time. I insist that this year you do not hold back and show all of your professors your full potential. You are a very intelligent young man and I do not want to see you getting bad grades. It is time to be you and not what you think people want you to be."
"It is your teaching that has made all of this possible Uncle Sev," said Harry. "Once you explained some of the techniques to me, it made potions more fun for me. It is a lot like cooking and I love to cook. As far as giving my full potential, I think I can handle that. Now that I no longer have to worry about my friends not keeping up, it will be easier to be me."
"We are here to see how you are doing," said Severus. "We were looking at the wards on the house and we have discovered something that doesn't sit right with us."
"What is wrong with the wards?" asked Harry. "I may not like staying here during the summer, but they are keeping me alive. If there is something wrong with them, then I could be in danger from the Dark Lord."
"That's just it," said Sirius. "There are no wards around the house. Both Severus and myself are accomplished Masters with wards. There are no wards around this house and there never was. Albus lied. You are being kept here against your will and the will of your blood relatives."
"Do you mean to say that I have been starved, beaten, mentally abused and everything else every summer for no reason what so ever?" asked Harry furiously.
"Pretty much," said Sirius. "We are here to fix that problem. Now that I am no longer a fugitive of the law, you are now able to come and live with me. I have spoken with Amelia Bones about this and the files state that I am to be your guardian. It was in your parent's wills. They never wanted you to live here. If I was unable to take care of you, Severus and Minerva were to do so."
"So you are telling me that Professor Dumbledore took it upon himself to place me where my mum and dad didn't want me to go," said Harry dully. "How is it that he was allowed to do something like this?"
"We do not know yet," said Severus. "By all rights when Sirius went to prison, you should have been turned over to me rather than Petunia and Vernon. We have Amelia looking into the matter for us right now."
"So how much longer do I have to stay here then?" Harry asked. "I mean this summer has not been too bad, but if I don't have to stay where I am not loved, I would rather be somewhere else."
"We are here to help you pack," said Sirius. "I have been given a full pardon and compensation for being sent to prison without a trial and for being innocent. Severus and I are going to take you shopping for your school supplies and some new clothes."
"I am tired of seeing you wear that fat lard of a child's hand me downs," said Severus. "If Lily were alive, she would strangle Petunia with her bare hands for the way you are being treated."
Harry stood up and started to pack his belongings. While he was doing so, he fired a question at the two men.
"Why are you two being so nice to one another?" he asked. "I thought you hated each other."
"We are no longer children," said Sirius. "When James and Lily died, we put our differences aside for YOU. I was an ass to Severus and I have made it my adult duty to not repeat my childish ways."
"I have never hated you or your father," said Severus. "I had a job to do from your mother. It was hard for me to treat you the way I did, but I did what I could behind the scene, to make sure that you were kept out of danger. The petty rivalry that James and I had in school was just that. We grew out of that once we became adults."
"You are a Death Eater though," said Harry. "Now that the Dark Lord is back, you have to start reporting to him. Plus, I know that Dumbledore is still telling you things about me."
"That is where there is a slight error," said Severus lifting his left sleeve and showing Harry his bare left arm. "I am not now nor have I ever been a Death Eater. I have worked for both the Dark Lord and Dumbledore in my years. Both pay me well for my services. My main job is to watch out over you. When it comes to you, I take my job very seriously. What is so interesting is that both Dumbledore and Voldemort, despite hating each other, want the same thing. Both insist that I keep you safe from the other. It is like neither wants you to be harmed by the other, yet both are hurting you more than they believe the other will."
"So where are we going?" asked Harry after he put the last few things in his trunk and closed the lid.
"We are taking you to Amos and Mary Diggory's house," said Sirius. "We can not bring you back to Grimmauld Place as that is where Albus has the Order. We spoke with Amos and Mary and of course Cedric and they agreed to take you into their home. We know how close you and Cedric are. Before we go though, I want to know why you are looking so sad. Your face gives off relief, but at the same time you have a look of sadness within you."
Harry pulled out three letters from his pocket and handed them to Severus and Sirius. They were from Ron, Hermione, and Ginny. Sirius opened Ron's letter and read out loud.
When we agreed to be your friend, we did not know that our lives were going to be constantly in danger. You are a danger to us. You are always getting attacked by the Dark Lord and we do not want to be a part of that anymore. We do not want to be your friend any more. When school starts, stay away from us. Do not write to us anymore and forget that we ever were friends.
Sirius was floored by the letter. He read it again to himself to verify that it was what was written. Severus opened Hermione's letter and read it out loud as well.
You never listen to what I tell you. You were told by me that it was a trap and yet you had to go and play the hero. I can not be friends with someone who doesn't do what they are told. Dumbledore told you to stay in the castle and do what you were told. You are always getting into trouble and you never listen to me. I told you so and I was right. You do not use your brain and I am tired of carrying you. Leave me alone when school starts and do not speak to me. I am no longer interested in being the friend of someone who draws so much negative attention to themselves. Stop being the hero all the time. It is rather getting old. Ron, Ginny, and I no longer want anything to do with you or this stupid war.
Your former friend
By now Sirius was seeing red. Severus paced a calming hand on his shoulder to steady him.
"What did Miss Weasley have to say?" asked Severus.
I had hopes that you and I would get married one day. You do not even bother to buy me anything out of the blue to show me that you love me. I feel like you are an albatross around my neck. I can no longer date someone who doesn't show me that he loves me. You went and got us into trouble at the Ministry of Magic. I never want to put my life on the line for you again. You and your money are not worth it. Stay away from me and leave me alone. I am going to find someone of my status to date instead of a half blood such as you. You don't even have that much money in your vault. I expected you to have enough money to make sure I lived like a princess. You are unable to do that. So I will tell you once more to just leave me alone.
"So she was never after your heart," observed Severus. "She was after your money. However, you do not seem that upset by her letter. Why is that?"
"Because I never loved her in that way," said Harry. "I saw her as a little sister not as a girlfriend. She has been hounding me for years to date her and I kept telling her no. She never listened to me. She just kept on and on about how we were going to get married and how because my family was rich that we would be high in society. Apparently her mum told her that my vault didn't have that much money in it. It is too bad for her that it is all that I have."
"That is not all that you have," said Sirius. "Harry your mum and dad were rich people. The Potter name is one of the oldest names in wizarding history. It is more powerful and influential than the Black family name. You have about nine different vaults that belong to you. The vault she is referring to is just your trust vault. You have much more that belongs to you once you turn sixteen. Once you turn sixteen you take on the mantle of Head of House of the Potter name. It gives you the full rights of any Head of House and you get to pick and choose where you want to live and who you want to marry and such."
"Well," said Harry after a moment of thought. "To bad the greedy harpy doesn't know that. Now she won't ever be rich and she will never get her hands on me or my money. Besides that, she is not who I am interested in anyhow. I would never have married her. She reminds me to much of Molly Weasley for me to marry her."
"Let's get you out of here," said Severus laughing. "We have a lot of work to do and little time to do it with. We need you out of here before Albus comes causing more trouble."
Harry smiled at the two men. Severus instructed Hedwig on where she was to fly to. Sirius shrunk Harry's trunk and handed it to him. Together the trio headed downstairs. Severus walked over and spoke to Petunia and Vernon.
"Harry will not be coming back here," he said. "You will also no longer be getting the stipend you have been receiving to take care of him. We have already put an end to that. You do not deserve to keep any of the money that you were given as you never did what you were supposed to do with it in the first place. However, we will let it slide. You are just lucky that Harry is doing as well as he is or I would have stripped the skin from your bodies as punishment."
"What money?" Petunia asked. "We do not receive anything for caring for him. We have to take it out of our own pockets. I am not about ready to spend our hard earned money on a child that we did not want in the first place."
"I suggest that you ask your greedy husband," said Severus. "Your family has been getting five thousand pounds a month for the care of Harry. Judging from what I can see, it has been spent on your son rather than on the child it was meant for. Tell me Petunia, did you ever read the letter from Dumbledore?"
"No," she admitted. "Vernon took it from me and he read it. He also burned it after he read it. I have never set eyes on the contents. Before you go, can you tell me what it said?"
"It said that as long as Harry had a good home that you all would be protected," said Severus. "Someone from the Order of the Phoenix would check this house twice a day to ensure that you and your family were safe and sound. In addition you and your family would receive five thousand pounds a month from Lily's vaults to care for him. That is plenty enough money to buy him clothes and food and toys and such. From what I can see of this house, you have never even had pictures taken of him. Even when Harry was in school, you still got your monthly stipend. Now you will never receive anything else ever again."
"Is this true Vernon?" asked Petunia horrified. "Have you been stealing Harry's money and keeping it for other purposes? You get paid plenty by Grunnings. You easily make enough to take care of all four of us. This payment for the care of Harry all but doubles your salary each month. You made me believe that we were barely making it and that it was because of Harry."
"I am the head of this house and we will do things my way," said Vernon. "I want you freaks out of our house and out of our lives. The letter stated that we will get five thousand pounds a month until the boy turns seventeen. I expect my payment on the first or Dumbledore will be in trouble."
"Then I suggest that you take it up with him," said Sirius. "I have already stopped the payments coming from his vaults. As his LEGAL guardian, I have the power to do so. When Dumbledore gets here, give him our best will you. I am sure that YOU will be in loads of trouble for not fulfilling your end of the bargain. I can only imagine what Dumbledore will do to you when he finds out that Harry is no longer living here and you have not done as he asked. That also goes for when the Dark Lord finds out about the abuse you heaped on an innocent child."
With that, Sirius and Severus took Harry away and they never looked back. As they were leaving they could hear the sound of flesh being struck and Petunia Dursley screaming at her husband for the injustice that she was forced to inflict upon her nephew. The trio arrived at the Diggory Manor in record time. Harry was greeted by Mary and Cedric warmly.
"Come on Harry," said Cedric. "I will show you to your new room. We put you in the room next to mine. I will help you get unpacked and ready. Sirius and Professor Snape said you will be living with us from now on. So we can get your stuff set up."
"Make sure you help him with the color scheme of his room and stuff," called Mary. "We want him to be as happy as possible here."
"I will get right on it mum," said Cedric. "I want Harry to know that this is his home as much as you do."
Mary smiled as the two teens walked off. Once they were out of earshot, she turned to Severus and Sirius.
"What are you going to do about Dumbledore?" she asked. "I don't want him coming here and trying to remove Harry from this house."
"Amelia Bones is already seeing to it that Dumbledore is backed off," said Sirius. "The wills of Lily and James were read and Albus doesn't have a legal leg to stand on. In fact he is going to be coming under many questions by the Ministry of Magic for blatantly disregarding the wishes of the Potters. Mary, we really appreciate you taking Harry in like this. If he needs anything at all, please send us an owl and we will reimburse you for your expenses."
"Do not worry about that," said Mary. "We wanted to take Harry in from the moment Lily and James died. It was because of Albus that we were not allowed. Harry does need new clothes though. He will also need his school supplies."
"We were going to take him when he got his Hogwarts letter," said Sirius. "He should be getting it any day now."
"It came a little while ago," said Mary. "So maybe you can take him tomorrow to Diagon Alley. Cedric can go with you so that he can pick up a few things that Harry might need while staying here at the house."
Harry and Cedric came back downstairs. Mary smiled at him and then handed him his letter. Harry opened it and read it out loud.
Dear Mr. Potter
We are pleased to announce the scores of your OWLS. These test results can be used to decide your future. Based on your scores, you have much to look to the future for.
DADA = O
Herbology = E
Transfiguration = E
Potions = O
History of Magic = A
COMC = O
Divination = E
Charms = O
Ancient Runes = O
Astrology = E
Congratulations on your ten OWLS.
"Hey," said Harry. "I passed every single subject. I didn't see that coming. I thought for sure that I was going to fail History of Magic. That has to be the most boring subject around."
"Congratulations Harry," said Cedric. "That is more OWLS than I got."
"Harry did you see what else was in this envelope?" asked Severus as he pulled out the school list.
"No," said Harry. "What was in it?"
Severus opened his hand and presented Harry with the Captain's badge of the quidditch team.
"Just like James," said Sirius. "Congratulations Harry. Tomorrow we are going to go and get your school supplies and such. Be ready at ten in the morning."
Harry grinned at everyone. He was happy with his results. Even the Head of Slytherin House was proud of him for his accomplishments.
The next morning, the group of men headed to Diagon Alley. Harry scanned down his list of things he needed. It did not say a whole lot.
"It all depends on what subjects you are going to go for a NEWT in," said Severus. "That is why the list is so uncompromising. It should tell you a list of books for each subject anyway in case you want to take the class."
"Well I am going to go for a NEWT in Potions, Transfiguration, Charms, DADA, Herbology, and Ancient Runes," said Harry. "I am going to drop Divination. I never liked History of Magic and Astrology is just not at the right time of the day. How I managed to get an E in Divination is beyond me. The examiner told me that I must be a natural. The only thing I did not pass was the crystal ball portion. I never did see anything in the smoke."
The group made their way to the bank where Harry got some gold out of his vault. He was met by Griphook who explained that they needed Harry to sign some paperwork to add his trust vault to his family vaults upon his sixteenth birthday. Harry quickly agreed and signed the documents. From there, the group went shopping. Harry got all of his school supplies as well as his course books and a completely new wardrobe. Severus treated them all to a lunch at one of the restaurants. Harry went to the pet store and bought Hedwig some more owl treats. He saw Hermione and Ron in the street and ignored them both. Ginny was looking at his new clothes and came up with a calculating look on her face.
"Forget it," said Sirius to her. "You have lost your chance. Harry is a VERY wealthy young man. He is richer than even I am. You lost any chance you had to be anything more than an aggravation to him now. Stay away from him and stay away from my house. You are no longer welcome in it."
Ginny burst into tears and fled behind Ron and Hermione. The group of four made it back to Diggory Manor. Harry and Cedric put his clothes and such away.
Harry's birthday rolled around. There was a small group of people around to celebrate it with him. Mary, Amos, Sirius, and Cedric all went out of their way to make sure that Harry had a birthday to remember. Minerva, Remus, Severus, and many other members of the Order sent him gifts and such. Harry smiled throughout the whole thing. He finally knew that people actually cared about him and he was going to relish the thought. These people did not expect anything out of him except for him to be happy and to be himself. This was something that Harry wanted for a long time. Harry was delighted by the sword that the goblins of Gringotts made for him. Griphook brought it to him personally. It was similar to Godric's sword, but the blade said Potter on it. Also included was a very old book that had things written in it from the first of the Potter line. In addition, Griphook handed him the signet ring that announced his title as Head of House for the Potter family.
Over the next few weeks, Harry read through his course books. He wanted to get familiar with the work that was coming up for the new school year. Cedric helped him where he could. The former Hufflepuff could still tell that there was sadness in Harry.
"Talk to me Harry," said Cedric on the night before they were due to leave. "What has you so sad?"
"It is Ron, Hermione, and Ginny," admitted Harry. "They said some very ugly things to me. They no longer want to be my friend because they said I am a danger to them. How am I supposed to be able to concentrate in school when I have to share a dorm with Ron?"
"Talk to McGonagall," said Cedric. "Tell her your concerns. She might be able to do something to assist you. Whatever you do, keep your head held high and know that you are a good person. They are just jealous because you are popular and they aren't."
"Thanks Cedric," said Harry. "I will do just that."
On the first of September, Mary and Cedric took Harry to the train station. Cedric helped Harry get his trunk onto the train and up onto the rack.
"We will see you for Christmas and Easter," said Mary as they stood beside the entrance to the carriage and were talking. "It is already set up with Professor McGonagall. She is happy that you are finally away from the Dursleys. She was against that idea from the start."
"Don't forget to talk with her about Ron, Hermione, and Ginny," said Cedric. "Show her your letters from them. She may be stern, but she is a good person and will hear you out. She will help prevent problems from occurring. Professor Snape will also be able to help you. If you really want additional coverage speak with Professor Sprout. She is very fair and very caring about all of the students. Write to me often so that I know that you are ok. Promise me that you will let me know how you are doing."
Harry smiled and promised as Mary hugged him. Cedric wrapped his arms around Harry in a warm manner before escorting the Gryffindor onto the train. Three pairs of eyes watched this scene with interest.
"It looks like Potter found someone else to pity him," said Ron. "Let's see how long he lasts without my family watching out over him. Now that I am a prefect and no longer his friend, I can make his life a living hell."
"You really should not abuse your position," said Hermione. "I may not be happy with Harry either, but there is no reason to make things harder on him than there already is. He is the one keeping Voldemort away from us after all. I say that we just leave him alone and let things run their course."
"I don't think so," said Ron. "I am going to give him a little payback. He pulled us through all of those adventures and we never got the fame or money that goes with it. I am going to punish him as often as I can."
"I am going to see to it that you lose that badge Weasel," said Draco standing there with his arms crossed. "Potter doesn't deserve half of what you are saying and going to do. He makes mistakes like everyone else, but that is no reason to use your position against him. The Potter name is very honorable even to us Slytherins. I may have my disagreements with Harry, but he is an honorable person. As I am witness to what you are planning, I will be talking to my Head of House as well as yours. You will not have that badge by the end of the feast in the Great Hall. You have my word on that."
"You don't know what you are talking about Malfoy," snapped Ginny. "He led us into danger. We should never have gone to the Ministry of Magic. I happen to agree with Ron and I will also be using my position to teach him a lesson. No one dumps me and lies to me the way he did."
"You were only there because you insisted," said Neville angrily. "I was with you if you care to remember. I know what really happened. He wanted to go alone. I will be reporting you to McGonagall as well. I am disgusted with you all for thinking about abusing your positions to hurt Harry. He is a good person that has done much for all of you. Where would half of you have been last year without him taking the brunt of Umbridge's hatred onto himself? He kept her ire on himself instead of people that are not pureblood. We know all about her. She hates anything that is not a pureblood and makes their lives miserable. Harry stopped her from using her position to make your life miserable Hermione as well as many of the half bloods and muggleborns. Where would you have been had he decided to not teach you all DADA? None of us would have passed our OWL without him. That includes the Weasleys."
"It was all of our choice to go with him," piped up Luna. "I should not be surprised by your attitude towards Harry. You have always been jealous of him Ronald. I will help Draco with his report of what you lot is planning on doing to Harry. So I will be speaking to Professor Flitwick about what you are saying and planning. I don't like it when people hurt my friends and Harry is the best friend anyone could ever ask for."
With that, Luna and Neville left to find the compartment that Harry was sitting in. Harry greeted his friends with enthusiasm. Draco smirked at Hermione and the Weasleys and sauntered off with the rest of his gang. He knew that his father wanted him to watch out over Harry. It was a job that he was doing since first year. Harry was reckless sometimes, but he was good at what he did. Draco rarely had to step up and defend Harry from danger. The few times that Harry actually was in danger, was due to the fact that there was little that Draco could do to help him. Draco sent a letter to Severus with Magus with regards to what they had overheard the trio talking about.
With Neville, Luna, Susan, Hannah, and a few others sitting with him in his compartment, Harry did not have any trouble on the train ride to the school. Draco and his Slytherin team were also patrolling the corridor often to make sure that unwanted visitors stayed away from Harry. When they got to the school, Harry stepped off the train and walked to the nearest thestral. He petted the creature for a moment before he got into the carriage and waited to be brought to the school.
AUTHOR'S NOTE – I had to end this chapter somewhere and I felt that this was as good a spot as any. Thanks in advance for the reviews and support. I want to set up the school idea before I get into the actual reason behind the story. Therefore, you will find out who is on what team and where everyone stands. Harry can see the thestrals as he did witness Lily Potter's death. I know that many of you will have questions about that. If you remember the flashbacks, they show the green light and Lily falling. Therefore, he witnessed her death and can see the thestrals. Thank you.