Sirius Black.

His escape from Azkaban hadn't taken long for him to be discovered by everyone; he knew they were searching for him in every corner there was. He didn't consider hiding behind the walls of his family's mansion; it was the first place they would look for him, he was sure of that. Instead, he showed up at the Weasleys' burrow, who came up with all kinds of ideas to hide him.

The plan of the twins who had just graduated from Hogwarts was considerable, although with many complications, it was still doubtful whether the rejuvenating potion would work and if it did, how long it would last. In a desperate measure like that, it turned out to be the best idea of ​​all. There was no question of where those two young people had gotten that potion from, they had simply already taken it. The effect was not instantaneous, it took almost half an hour.

He had only been here for two days, being the man he once was, when he still had a brother and a family, not the Blacks, the Potters. Arthur made him see reason that he couldn't try to see his godson yet, Hogwarts security had increased since his escape and the presence of Dementors around them, he had to be patient, was what Molly told him. He was still thinking about Remus, about James.

He was still an old man beneath that youthful image, but those Weasley brothers insisted he go to his "job" as objects of pranks, telling him he should behave like a young man and not like an old alcoholic. There was nothing interesting there, except children and teenagers milling around everywhere. It wasn't cold, but the sight chilled him to the bone. He stood there, unsettled by that black hair, those grey eyes, and that amused smile that reminded him of him, of Regulus. No, it couldn't be his brother; there was no trace of anything impure on his wrist, and his brother should be a grown man by now.

He's drunk a potion that made him young again. He thinks he's seen his brother, Regulus Black, but it's actually his nephew, Regulus's son.