Details of Peter Capaldi's final outing in Doctor Who have been revealed as the first trailer for the Christmas special was released online.
The one-minute clip for the episode, titled Twice Upon A Time, sees Capaldi and the First Doctor team up.
It features the return of Pearl Mackie as Bill Potts, who had seemingly left the show at the end of series 10.
The clip also showed a guest appearance from Mark Gatiss, who plays a World War One soldier called The Captain.
The release of the trailer coincided with the cast appearing at Comic-Con in San Diego on Sunday, where they talked about the upcoming episode, the last series and looked back at Capaldi's time on the sci-fi drama.
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