The BBC spoils Christmas by revealing here http://www.bbc.co.uk/news/entertainment-arts-22741493 that:
'Doctor Who star Matt Smith is to leave his role as the Doctor at the end of this year, the BBC has announced.
After four years as the Time Lord on the BBC One show, viewers will see Smith's Doctor regenerate in the 2013 Christmas special.
The 30-year-old actor said working on the show had been "the most brilliant experience".
Doctor Who marks its 50th anniversary in November with a special episode, which Smith has already filmed.
The BBC said Smith's "spectacular exit" was yet to be revealed and would be "kept tightly under wraps".'
Thanks BBC, not much of a surprise now and we'll done on keeping the regeneration 'tightly under wraps'.