Yep... you hear me correctly... the Doctor will be appearing on our screens twice on Christmas day, how exciting!
As well as the eagerly anticipated 'Voyage of the Damned', comedian and actor Ricky Gervaise (The Office) is doing a 'Extras' Christmas special in which David Tennant is starring. In the video below, you will see a snippet of the teaser in which Tennant, as the Doctor, can be seen on two occasions.
At the end of the teaser, I've put the two clips together so you can see him better.
Edit: 26th November
A photo of the Extras Christmas special has just been released with none other than David Tennant as the Doctor hanging around in the background. This kinda suggests that maybe he will have quite a large part? Or at least, bigger than just a single scene.