Current Doctor Who star Matt Smith is to leave the BBC television show at the end of this year.
After four years as the Time Lord, viewers will see Smith's Doctor regenerate in the 2013 Christmas special.
Doctor Who marks its 50th anniversary in November with a special episode, which Smith has already filmed.
When Smith, 30, first stepped into the Tardis as the 11th Doctor in 2010, he became the youngest actor to play the role.
He said working on the show has been "the most brilliant experience".