By Mark Armstrong
Updated February 21, 2003 11:00 AM

Sir Michael Gambon has a prestigious new title: headmaster of Hogwarts.

Ending months of speculation, the Irish-born actor was officially tapped to replace the late Richard Harris as Professor Albus Dumbledore in “Harry Potter and the Prisoner of Azkaban,” the third installment in the boy wizard’s big-screen franchise, Warner Bros. announced Friday, according to the Associated Press.

Gambon, 62, who recently appeared in “Gosford Park” and played President Lyndon B. Johnson in the 2002 HBO movie “Path to War,” was one of several names that surfaced as a possible Dumbledore candidate, along with Christopher Lee, Ian McKellen and Peter O’Toole (who was a longtime pal of Harris’s).

But producers remained secretive about who would fill the very big shoes of Harris, 72, who died of Hodgkin’s disease in October. The actor — who starred in both “Harry Potter and the Sorcerer’s Stone” and last year’s sequel, “The Chamber of Secrets” — initially had signed for the third movie and hoped to recuperate in time for shooting to begin.

Production on “The Prisoner of Azkaban” is now underway in London, with Alfonso Cuaron (“Y Tu Mama Tambien”) directing. (Cuaron replaces Chris Columbus, who was behind the camera for the first two films.)

Daniel Radcliffe, meanwhile, is returning as Harry Potter, joined by Hogwarts regulars Rupert Grint and Emma Watson. Warner Bros. also recently announced the addition of Gary Oldman, who will play the mysterious character Sirius Black — the prisoner of Azkaban.

For Gambon, Dumbledore will be one of his most high-profile roles, following an accomplished career on stage and screen. His other film credits include 1992’s “Toys” with Robin Williams and Tim Burton’s 1999 film “Sleepy Hollow.” He was knighted by Queen Elizabeth II in 1992.