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 (film series) to be re-cast for the third instalment, "Harry Potter and the Prisoner of Azkaban". David Heyman and director Alfonso Cuarón chose Michael Gambon to portray the character of Dumbledore, which he did for all succeeding films. Notable recurring cast members include Helena Bonham Carter as Bellatrix Lestrange, Warwick Davis as Filius Flitwick, Ralph Fiennes as Lord Voldemort, Brendan Gleeson as Alastor Moody, Richard Griffiths as Vernon Dursley, Jason Isaacs as Lucius Malfoy, Gary Oldman as Sirius Black, Fiona Shaw as Petunia Dursley, Timothy Spall as Peter Pettigrew, David Thewlis as Remus Lupin, Emma Thompson as Sybill Trelawney, Mark Williams as