As widely rumoured, the key role of Sirius Black will be played by Gary Oldman.
And Timothy Spall will bringing Peter Pettigrew to life.
All three are well-known British actors who've starred in many films and TV shows.
They join David Thewlis - confirmed as Remus Lupin in January - and Daniel Radcliffe, Rupert Grint and Emma Watson from the first two films.
What about Cho Chang?
Fast Show fave Paul Whitehouse has scooped a minor role too. He plays a knight from one of the paintings Sir Cadogan.
At the moment there is no news on Cho Chang, but some other Hogwarts students have been cast and will be revealed soon.