Sirius Black adopts Harry Potter at 13 AU and realizes that he is utterly unequipped to deal with talking about teenage urges by the time Harry starts dating Cho.
"BUT I WAS DOING THE THING AROUND THAT AGE, MOONY. YOU WERE DOING THE THING"
"I did no such—"
"BECKY FROM HUFFLEPUFF AND THAT BLOKE ON THE RAVENCLAW QUIDDITCH TEAM, MOONY"
"Wait. How did you—"
"THE POINT IS YOU HAVE BOOKS ABOUT THIS. TELL ME YOU HAVE BOOKS. BOOKS ABOUT THE THING."
And that’s how a bedraggled Remus and a wide-eyed Sirius awkwardly stumbled their way through The Talk with Harry during the holidays.