I know I should be focusing on TDTCE but this little plot bunny wouldn't leave me alone. Thanks to Pup03 for the idea!

Note:
Severus was in the year above James and Lily.
Harry was 12 instead of 11 when he first started Hogwarts.
Albus was born in 1881 (as in reality.) but he stopped aging in 1919 because of a magic incident that he nor no-one else could reverse.

Remus' Mate

Remus stiffened as he heard footsteps near his carriage and held his breath but kept his eyes shut as he hear three students enter his carriage and sit down. He sniffed the air, he could tell there were three students, young as well no older than 13 but there was something else a smell stronger than all of that permeating the air. Remus breathed in, the smell was addictive and he drank in the taste. Remus fell back to sleep confused at the smell and what it meant, he was awoken not long after by a scream he opened his eyes and jumped up whipping out his wand upon seeing the attacker he shouted "EXPECTO PATRONUM" and the dementor glided away. He turned to face the troubled teens and was instantly assaulted by the smell once again, this time though he was aware of the source. He looked at the boy passed out on the floor and his entire body tensed then relaxed. He fell silent, the girl was shaking the boy and the other boy was clutching (judging by the matching hair colour) his sister. Remus reached into his pocket and pulled out several bars of chocolate, he handed them to each person.
"Eat it, it will make you feel better, trust me, I'm the new DADA teacher. Remus Lupin at your service." The two gingers (Weasleys he was guessing.) immediately started eating the chocolate but the girl didn't move.
"Please Sir, was that a dementor?"
"Yes. Eat the chocolate while I wake up young-"
"Harry sir Harry Potter is his name."
"-Harry. Please give me some space to work on him." After the girl sat on the bench and began her chocolate Remus knelt next to Harry. Harry Potter? James and Lily's son? As he knelt the smell grew stronger as did his arousal. Oh dear lord, he'd mated with a teenager? He nevertheless got to work whispering spells over Harry's limp body. The boy eventually began to squirm and his eyes fluttered open to reveal to Remus glittering emerald orbs. Remus inhaled strongly, regretting it almost immediately when he became dizzy with his arousal and so thrust a packet of chocolate onto Harry's lap with a curt
"Eat it, you'll feel better. I'm going to talk to the driver." And he left the compartment. Upon entering the hall, away from the dizzying odour of his "mate" he was able to think clearly, he had to talk to Dumbledore. He sent a patronus requesting meeting as soon as he was in the castle, and want to talk to the driver.

MEANWHILE

Harry was leaning against Hernione's seat - still on the floor, eating his chocolate.
"So who was that guy?" He asked with his mouth full.
"The new DADA professor - Remus Lupin." Hermione replied with a disapproving look.
"He's hot."
"WHAT? Harry, mate he's a teacher, you're a student! That is totally creepy. Besides he seemed quite shabby." Ron sounded flabbergasted.
"Oh because you're one to talk!" Harry said angrily in reply. Ginny looked upset
and Ron face was aflame with anger.
"OY- just because I'm not as rich as you doesn't mean you can - "
"Ok boys calm down. Harry that was uncalled for and Ron don't be so defensive. You're both upsetting Ginny." Hermione had stood up. The boys sat down and looked in different directions without talking for the last 15 minutes of the train journey. When they finally reached the school in the mysterious carriages they had resorted to speaking to each through Hernione and upon reaching the great hall they sat on either side of Hermione, with Harry mainly talking to Seamus instead.

Once finally reaching the school, Remus immediately swept into Dumbledore's grand study.
"Albus! Albus!"
"Remus, my dear boy! What is the rush to meet with me?"
"Albus, something terrible's happened-I've done something terrible!" Remus was distract at this stage and Albus guided him to the leather sofa in the corner of his private study (behind the headmaster office).
"Remus, nothing so bad could have happened on the train - other than the almost dementor attack."
"Albus I've found my mate!"
"Remus that's not terrible - that's great news, have you made plans to actually mate yet!"
"Albus that's only half of it - when you hear you'll know why I haven't made plans to mate."
"Well then explain."
"It's a student, a young student."
"How young?"
"Third year."
"Remus, who is it?"
"Harry." He didn't have to say anything else, they both knew who he meant.
"Remus, it's not as bad as you think - he's 14. Only three years from being of age and you know he's only two years until he's legally of sexual age, and the government will allow it as he's mated to a magical creature."
"But isn't that sick or disturbed?"
"No, you're mated and I fully support you and him together. I'm assuming your the dominant/alpha in the relationship?"
"Of course!"
"Then your lucky it's Harry, he needs strict boundaries so you'll be perfect! "
"I'm not strict?!"
"Take it from a submissive of a vampire, you are one of the strictest dominants I've ever met."
"But you're old enough to be my grandfather - surely I've never dominated you? "
"I'm strongly submissive Remus, why do you think I'm so attracted to Severus? And he will at some point be old enough to be your grandfather since he is never aging."
"But you're still aging aren't you?"
"I stopped aging a long time ago due to a magic accident. Severus has now been on this earth for 37 years despite looking 26 and I am despite being born in 1881, 38 years old."
"But you look, no offence but..."
"It is a glamour to conceal from Voldemort and our relationship to be kept on the downlow."
"Can you show me?"
Dumbledore smiled and with a flourish his long white beard shortened to stubble, his hair disappeared then reappeared from the roots, first black before suddenly changing to bleached blond white. His wrinkles almost totally disappeared and he became more solid although shrinking with his muscles growing until the changes stopped altogether and his true self appeared. He was quite short, compared to Severus and Remus' long lanky forms he would appear as a dwarf despite still being 5"8. His muscles were more shapely and toned and there seemed to not be an inch of fat on him. His face looked 50yrs younger with strong cheekbones and he had three earrings in one ear and was Dumbledore wearing nipple rings?! The biggest shock though was the bleached hair. Remus couldn't remember ever being this shocked.
"What the hell happened to your hair and are they actual nipple rings?"
"Umm well Severus did my nipples but he doesn't know about my hair. You see -"
A startled shriek was suddenly heard behind them. Albus winced.
"ALBUS!? WHAT ON THE EARTH HAPPENED TO YOUR HAIR!" Severus marched forward and yanked Albus up with a firm grip to his upper arm.
"Your young mate has been sent to the hospital wing by me under the pretence if needing to be checked out after the dementor, but to be honest with you, he smells absolutely perfect - I had to remind myself he was yours to stop me from ripping his clothes off. I was afraid if he went to the Great Hall with all those teenage hormones, we'd have a riot. You should check on him while I talk to Albus here." Severus' hand had moved to Albus' neck and he was gripping hard. Albus winced once again. Remus nodded and left.
Severus turned his head back to a squirming Albus and raised an eyebrow dangerously.
"Your hair had better wash out. Explain."

This is a tester chapter please review and tell me what you think and if I should continue!