You were a werewolf. One of the professors had found you in the forest half dead and they brought you to the castle. There wasn’t any more dorms so they put you in with Cedric Diggory.

You were laying in Cedric’s bed asleep and then Cedric walked in not knowing you were there. “ God, what’s that smell?” Cedric said and then he noticed you. You were dirty, full of wounds and bruises and your hair was tangled.