Albus is an old man now, and finally ready to move on. He dies peacefully in his sleep, unafraid because his father’s always told him that there’s no reason to fear death.
When he opens his eyes, the first thing he sees is a face. He’s seen it in pictures before, young and smiling amidst his three best friends, laughing at Albus’s grandparents’ wedding, newspaper clippings showing him as an escaped prisoner. He recognizes this man to be his dad’s godfather, the brave man that Harry’s said grew up in a horrible house and would’ve given his life to keep his best friends safe without a second thought, who lived twelve years with dementors, escaped and was forced to live quietly in his old, dark house, who died so unexpectedly at the hand of his own cousin. He knows that this man is brave and valiant and bold.
In the moment it take him to recognize this, the handsome face cracks into a smug smile. Sirius Black opens his mouth, and Albus is ready, sure he’s going to say something simple and beautiful and wise; and then Sirius says, “Albus Snivellus Potter.”