Disclaimer: I don't own Harry Potter or any character from the series.
Disclaimer 2: This fic is based on 'A Sirius Matter', by witowsmp.
Uncovering the Truth
Hermione Granger couldn't help but notice how sad her boyfriend seemed to be. "Any problem, Harry?"
"Hermione, Snape was really on our side." He said. "And I'll never find out why."
"Don't be so sure, Harry." She said with a smile.
"How not?" He was now confused. "Snape and Dumbledore were the only people who knew the truth and both of them are dead."
"Have you never read Hogwarts: A History?" She asked as usual. "All deceased Headmasters appear in paintings at the Headmaster's office to give advices to the current Headmaster. You wanna talk to the deceased Headmaster Dumbledore? Go to Headmistress McGonagall and talk to his portrait."
Happy with the possibility of finding out the truth, Harry gave Hermione a big kiss and ran towards the Headmistress' office. "Mr. Potter, what can I do for you?" Asked the Headmistress.
"Headmistress McGonagall, may I talk to Headmaster Dumbledore's painting?" He asked.
"Certainly, Mr. Potter."
"Hello, Harry." Albus Dumbledore said.
"Professor Dumbledore, now that Riddle is dead, may I know why you trusted Snape so much?" Harry asked.
"I'm sorry, Harry. But I promised Severus I'd never tell anyone." Dumbledore solemnly answered.
"You might have promised, Albus, but I haven't." Said another portrait. "I'd be most glad in telling what made a fellow Slytherin fight valiantly against that monster."
"Sorry, but I don't believe we've already been introduced." Said Harry.
"Where are my manners?" The Headmaster said. "I'm Phineas Nigellus Black, the last Slytherin to ever become Headmaster of Hogwarts."
"Yes, I'm an ancestor of Sirius Black, and I'm sorry to know that the last male Black in the family died." Phineas said. "But I believe you came here to talk about Severus Snape."
"Yes, I want to know why Headmaster Dumbledore trusted him so much."
"Severus Snape loved your mother and wanted to protect her."
"What?" Harry was shocked. "But it was his fault that Riddle wanted to kill her!"
"When he told about the prophecy, he didn't know it included his family." Phineas said. "Did you know both your mother and Severus had a doe as their Patronus?"
"I don't believe she ever knew about Severus' feelings." Phineas said. "He's never been able to express them to her."
"Excuse me, but I have a lot to think about now." Harry said and then left.
I'm sorry if you find it too short.