Matt Smith's Doctor Who Co-Star Alex Kingston 'Knew He Wanted To Leave'

Alex Kingston has revealed that she knew Matt Smith was thinking of leaving Doctor Who prior to his resignation, and conceded that it "becomes very difficult" for actors to depart such high-profile roles if they stay in them for too long.

Kingston has enjoyed a recurring role in the BBC series and previously won acclaim for her recurring stint in US medical drama ER.

Appearing on The One Show last night, she said that a conversation she had with Smith meant she was not shocked by news that he will step down from the role later this year.

WATCH: Matt Smith explains why he has to hand the role over to someone younger...

Matt Smith with a newly-shaved head (WENN)

"I wasn't surprised, because he and I had a chat," she said. "At some stage, you have to move on and we did discuss when would be the right time in a young actor's career [to leave] if they were very associated with a particular role."

She added: "You have to move on, otherwise it becomes very difficult."

Speculation on who will replace Smith has been rife, and bookies currently expect Ben Daniels to step in. Paddy Power list him as 2/1 favourite, narrowly ahead of Chris Addison on 7/2 and Chiwetel Ejiofor on 9/1. The top-ranked female contender is Olivia Colman on 20/1 with Miranda Hart on 33/1.

Alex Kingston on the red carpet in 2011 (WENN)

In a statement, Matt Smith said of his departure: "It's been an honour to play this part, to follow the legacy of brilliant actors.

"But when you gotta go, you gotta go and Trenzalore calls. Thank you guys.”

Executive Producer Steven Moffat added: "Great actors always know when it's time for the curtain call. So this Christmas prepare for your hearts to break as we say goodbye to No. 11. Thank you Matt – bow ties were never cooler."

Matt Smith dangles over Trafalgar Square for Who filming

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