The latest from the official Tennant page:
Today saw the first day of filming for the Doctor Who 50th Anniversary Special and the first fan photo has reached the internet.
Witnesses reported that David Tennant, Matt Smith and Billie Piper were all on set today on location in Neath. Other witness reports and pictures also revealed the presence of the Tenth Doctor's TARDIS and a medieval style tent.
The picture below, though distant, shows David Tennant standing to the right of the group with Billie Piper beside him.
David Tennant, Billie Piper, Matt Smith, Jenna-Louise Coleman and John Hurt have all been confirmed for the celebratory episode, and last night the BBC confirmed that Gavin And Stacey star Joanna Page would also be joining the cast. Today it was announced that the classic foes the Zygons would be returning to face the Doctor for this episode.