Lithgow has been cast as the beloved Hogwarts headmaster, Albus Dumbledore, who was previously played by the late Richard Harris in the first two movies before Michael Gambon took over the part for the latter six films. In February, Lithgow told ScreenRant that the role "came as a total surprise," adding that he is "very excited" to get started.

Harry Potter star Nick Frost first gained fame for his collaborations with Edgar Wright, appearing in Shaun of the Dead and Hot Fuzz. His other roles include Kinky Boots, Grindhouse, and The Adventures of Tintin: The Secret of the Unicorn.

The Harry Potter HBO series has been all over the place when it comes to casting choices, but this one actually makes sense.