Doctor Who Christmas special: Watch Matt Smith's final outing in new trailer The BBC has released the 30 second trailer for the Christmas special, entitled "The Time of The Doctor," due to air on Christmas Day. Scroll to see the trailer below The episode will be Matt Smith's last outing as the Time Lord before twelfth doctor Peter Capaldi takes his place. The trailer opens ominously with narration from Jenna Coleman as Clara Oswald, before a mysterious woman says the "siege of Trenzalore is now begun," where Smith's Doctor is set to regenerate into a new body. As a house explodes into flames, a Dalek can be heard saying: " The Doctor is regenerating." Jenna Louise Coleman spoke earlier this week about appearing alongside her co-star Matt Smith for the last time. The actress said it had been an "emotional" farewell on set, adding she had become attached to the actor. "It's such a strange relationship because it really is just the two of you," she said. Doctor Who writer Steven Moffat also said recently he thought Peter Capaldi's incarnation of the doctor was "worlds away" from his Thick of It character Malcolm Tucker. Speaking to SFX magazine, he said: ""I'm confident that we'll sell this Doctor to our existing audience and he will be different enough that people won't just be miserable that they're missing Matt."