Mark Gatiss will play a World War One soldier known as 'The Captain' in the 'Doctor Who' Christmas special.

The show's writer will take on his fourth role in the BBC sci-fi series when he appears on screen in Peter Capaldi's final episode, which will be called 'Twice Upon a Time', in December.

No other details about 'The Captain' were revealed when the character was announced during a cast panel at San Diego Comic Con on Sunday (23.07.17).

Mark has previously played a mutated scientist called Professor Lazarus in 2007, voiced World War II pilot 'Danny Boy' in 2010 and 2011 and played Gantok in 'The Wedding of River Song' in 2011.

And he recently admitted he has no idea if he will remain as a writer when Steven Moffat steps down as showrunner and Chris Chibnall takes over.

He said: "I've no idea. It's a funny thing, an end of an era.

"Obviously working very closely with Steven I feel it more than when Russell [T Davies, previous showrunner on' Doctor Who'] left. I suppose there was more of a sense of continuity there, but I've no idea.

"I've had a fantastic run on my favourite show, so if I don't do anymore then I'm perfectly sanguine. But who knows?"

Meanwhile, it was also revealed that Pearl Mackie will make an appearance in the upcoming Christmas special.

The actress' alter ego Bill Potts was converted into a Mondasian Cyberman in season 10 of 'Doctor Who', much to the shock of fans after she had seemed to die, and the Time Lord's companion will be back for the upcoming episode.

However, it has not been made clear exactly how Bill will make her return.

A teaser trailer for 'Twice Upon A Time' also debuted at Comic Con on Sunday.