Pottermore: "Shortly before Remus Lupin’s fifth birthday, as he slept peacefully in his bed, Fenrir Greyback forced open the boy’s window and attacked him. Lyall reached the bedroom in time to save his son’s life, driving Greyback out of the house with a number of powerful curses. However, henceforth, Remus would be a full-fledged werewolf. Lyall Lupin never forgave himself for the words he had spoken in front of Greyback at the inquiry: ‘soulless, evil, deserving nothing but death’. He had parroted what was the common view of werewolves in his community, but his son was what he had always been - loveable and clever - except for that terrible period at the full moon when he suffered an excruciating transformation and became a danger to everyone around him."