your former DADA teacher, Mr Lupin, got fired, so the headmaster had to hire a new one. you were expecting to see an old man, but instead of that, being late to class, you see a ginger long-haired young man sitting on his desk and grinning widely, being in a good mood. "Sup, class. I'm your new DADA teacher, William Weasley." Weasley? it seems like he's the older brother of your fellow friends Fred and George. "Today i'll be teaching about- Oh- someone's late! com'ere, kiddo."