A familiar face showed up during the filming of Doctor Who's special one-off episodes... and it was even more of a shock to that time-traveling shaman, the Doctor, than it'll be to you. Spoilers, yo!
Tons of details on the new filming come from the Doctor Who Forum geniuses, including Scooty, Alun.Vega, Lucky Lady, Victoria Feller, Spaceygal, The Gather and Ahremsee.
Tennant filmed a scene where he comes out of the TARDIS with new companion Lyndsay Duncan, a male companion, and someone else. They're on the snowy streets of a futuristic city, featuring signs that say it's a low-emissions zone, and hydrogen-powered vehicles only are allowed. And "Congestion-Charging Central Zone: 3000 Yen Fine Per Day." It's snowing, and the Doctor says he loves snow. But the male companion says it's not snow. (Again?)
Oh, and there's a cute friendly robot with "GADGET" written on its front, who rolls up to the Doctor and talks to him in a non-threatening way. (Could this be the same robot we saw going through the explosion in the splodey sequences filmed earlier?)
The Doctor points to a nearby building with his sonic screwdriver, and Lindsay goes over there. Then the Doctor sees something and it shocks him so much he sinks to his knees and gasps, slumping against the TARDIS. Then he rushes inside the TARDIS and slams the door. But one eyewitness says they filmed another version of the scene, where the Doctor just walks into the TARDIS. In any case, could his shock have something to do with the reapparance on the scene of Ood Sigma? Ood Sigma turned up at the end of the scene, but didn't have much interaction with the other characters. And here's a video. (There are way more pics at the various links above.)
Top image by Alun.Vega. [Planet Gallifrey, thanks so much Scooty, Alun.Vega, Spaceygal, Victoria Feller, Lady Luck, The Gather, Ahremsee and everyone else!]