Complex sentence: Despite missing out on the first film, in 2004 Thewlis was cast as Remus Lupin in "Harry Potter and the Prisoner of Azkaban" without having to audition, as he was director Alfonso Cuarón's first choice for the role.
Split into simpler sentences: Despite missing out on the first film, in 2004 Thewlis was cast as Remus Lupin in "Harry Potter and the Prisoner of Azkaban". He did not have to audition as he was director Alfonso Cuarón's first choice for the role.