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.
Gatiss described the Christmas special as being “a Christmas episode without being overtly Christmassy – it’s very happy-sad”.
He added: “[It’s] a fantastic episode and we had a great time doing it. It was a lovely way out.”
It will be the third time the Sherlock actor and writer has appeared on Doctor Who, after previously starring in episodes in series three and six.
Mackie also confirmed the festive episode will be her last appearance on the show.
