Harry Potter and the Prisoner of Azkaban attacked by a big black dog, which Harry has seen several times before. The dog drags Ron through a tunnel under the Whomping Willow into the Shrieking Shack. Harry and Hermione follow, and there is a brief standoff when they find Ron with Sirius Black, who has transformed from the dog. Lupin enters, and they explain the situation to Harry and his friends: Lupin is a werewolf, which led to his friends James Potter, Sirius Black, and Peter Pettigrew becoming animagi. Lupin explains that Scabbers is Pettigrew in his animal form; he has been hiding from Black, whom he had
Harry Potter and the Prisoner of Azkaban (film) and Sirius. The present Harry realises that it was actually him who conjured the Patronus, and does so again. Harry and Hermione rescue Sirius, who escapes with Buckbeak. Exposed as a werewolf, Lupin resigns from teaching to prevent an uproar from parents. Sirius sends Harry a Firebolt broom, who happily takes it for a ride. With "Prisoner of Azkaban", production of the "Harry Potter" films switched to an eighteen-month cycle, which producer David Heyman explained was "to give each [film] the time it required." Chris Columbus, the director of the previous two films, decided not to return to helm the