Peter Capaldi is leaving 'Doctor Who' - and here's who could replace him

LONDON - Peter Capaldi is to leave "Doctor Who" this December after four years as the Time Lord in the BBC's iconic sci-fi franchise.

Capaldi will retire from the Tardis after the 2017 Christmas special. He first took on the role in 2013, replacing Matt Smith, who has gone on to star in Netflix drama "The Crown."

Capaldi announced his decision on BBC Radio 2 on Monday evening. He said:

"One of the greatest privileges of being Doctor Who is to see the world at its best. From our brilliant crew and creative team working for the best broadcaster on the planet, to the viewers and fans whose endless creativity, generosity and inclusiveness points to a brighter future ahead. I can't thank everyone enough. It's been cosmic."

The actor's departure will coincide with that of showrunner Steven Moffat. Moffat will be replaced by "Broadchurch" creator Chris Chibnall next year.

Capaldi's final series as the Doctor will begin in April, followed by the Christmas special when the "Doctor Who" regeneration will take place. Bookmakers are already speculating on who could replace him as the Time Lord.

Ladbrokes has made "James Bond" star Ben Whishaw the favourite to take over the time-hopping drama, according to the Daily Mirror. Other candidates include Richard Ayoade, Rory Kinnear, Miranda Hart, and David Harewood.

"Fingers are firmly pointing at Ben Whishaw," Ladbrokes' Jessica Bridge said. "He's favourite to swap MI6 for the Tardis sooner rather than later."