Sir Ian McKellen, 63, who plays the wizard Gandalf in the "Lord of the Rings" trilogy, is starting to be typecast.

Britain's ITV reports that the actor will take over for the late Richard Harris as Professor Albus Dumbledore in the next -- and third -- movie about J.K. Rowling's boy wizard, "Harry Potter and the Prisoner of Azkaban."

Warner Bros. (which, like PEOPLE, is part of AOL Time Warner) has reportedly been struggling to find a proper replacement for Harris, who died of Hodgkin's disease this past October.

The studio and representatives for McKellen have not confirmed the casting, though ITV says Warners will make an official announcement sometime after Jan. 1. "The Prisoner of Azkaban" is due to begin filming in England in March.

McKellen, best known as a classical stage actor in his native England and on Broadway, was suddenly catapulted to international fame with last year's release of "Lord of the Rings: The Fellowship of the Rings."

The current "Lord of the Rings: The Two Towers," which is a box-office smash, has confirmed his star status, and next year he will be seen in "Lord of the Rings: The Return of the King."