Peter Capaldi is the new Doctor Who.
Peter Capaldi is the new Doctor Who. ( BBC America )

The Doctor has regenerated.

Scottish actor Peter Capaldi ("In The Loop," "World War Z") has been cast to headline the sci-fi juggernaut "Doctor Who," it was announced on Sunday.

Capaldi will take over the role after departing star Matt Smith makes his final appearance in the show's December Christmas special.

The highly-anticipated casting was announced during a live special that aired on BBC America and BBC One on Sunday.

"It's so wonderful not to keep this secret any longer," said Capaldi, a lifelong fan of the show. "I haven't played Doctor Who since I was 9 on the playground."

Capaldi, 55, becomes the 12th actor to play the Doctor since the cult show debuted in 1963 with star William Hartnell and the fourth Time Lord since executive producer Russell T Davies rebooted Doctor Who in 2005, following Christopher Eccleston, David Tennant and Smith.

Executive producer Steven Moffat had considered Capaldi when they were casting the 11th Doctor. "There comes a right time for the right person to play it," he said.