Just found out this morning that Tennant is coming up to London on Friday to shoot a scene with Billie Piper. And it is literally just the one scene. Episode 4.18, Scene 163 to be precise. They're going to be out on location in a reasonably public place so there's some chance of photos but I don't want to be too specific in case the descent of hordes of 'Doctor Who' fans prompts anyone to try and find out where the information originated.
No idea what the scene actually entails but the Call Sheet lists the characters as "The Other Doctor" and "Rose Smith" so draw your own conclusions!
I am the first to admit this may be rubbish, but it has something that tells me it could be true!
Rose Smith? - Has Rose Tyler married the other doctor?
Sarah Janes cameo farewell is scene 153 and the bookstore is scene 155, so scene 163 isn't too high!