Steven Moffat has teased Nicola Coughlan will "break your heart" in the 'Doctor Who' Christmas special.

Steven Moffat has written the Doctor Who Christmas special

Steven Moffat has written the Doctor Who Christmas special

The 62-year-old writer didn't want to share too many details about the festive episode, which is titled 'Joy to the World', but after the 'Bridgerton' actress was confirmed to appear alongside Timelord Ncuti Gatwa, he has promised fans she will be "wonderful".

Speaking on 'Ireland AM', he said: "Nicola is wonderful in it, she will break your heart.

"I'm not allowed to say anything about it. At least I think I'm not allowed to say anything about it so I'll just shut up."

Steven was showrunner on 'Doctor Who' from 2010-17 and he admitted it "wasn't as weird as it should've been" to return to the beloved sci-fi series, which currently has Russell T. Davies at the helm.

He said: "It was just fun and it was quite nice that I had my old job back for exactly one episode and then I could go lie down. Russell [T Davies] has to keep toiling away all the time, constantly."

Russell has previously promised the Christmas special will be "mad".

He said in a behind-the-scenes video: "I can't give away much more but work has begun on it already, and it's mad, it's one of the maddest Christmas specials you'll ever see.

"It's epic, it goes to so many different places. And it's a great story of who the Doctor is when he's alone."

When Nicola's casting was first announced, Russell praised the 'Derry Girls' star for "bringing joy" to the set.

He said: "This has been the most brilliant shoot, with Nicola lighting up the set and bringing joy.

"From Derry, via Bridgerton, to the TARDIS, it’s the trip of a lifetime.”

Nicola added: "I’ve been a fan of Ncuti Gatwa for some time and getting to share the screen with him as the Doctor has been an absolute joy."

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