The new star of Doctor Who will be revealed in a special live programme on Sunday, the BBC has announced.
The half-hour show, presented by Zoe Ball, will feature an interview with the new lead, as well as 11th Doctor Matt Smith and executive producer Steven Moffat.
"The decision is made and the time has come to reveal who's taking over the Tardis," Moffat said.
"For the last of the Time Lords, the clock is striking twelve."
Doctor Who Live: The Next Doctor, is on BBC One at 7pm on 4 August.
According to the official announcement, Ball "will unveil the 12th Doctor in the first ever interview in front of a live studio audience set against the backdrop of a swirling vortex, amongst Daleks and the Tardis".
Smith, who has played the Time Lord since 2010, announced in June that he would be bowing out in this year's Christmas special.
The announcement sparked much speculation about who might take over, with Peter Capaldi, Ben Daniels, Rory Kinnear and Ben Whishaw among the bookies' favourites.
Ben Stephenson, BBC drama controller, said: "Amongst all the speculation and betting, there has been lots of fun and intrigue at work as we've been using the codename Houdini as a decoy.
"It's the biggest secret in showbiz, even those working with the new Doctor on other projects at the moment have no idea they are in the presence of the 12th incarnation."
Doctor Who marks its 50th anniversary on 23 November with a special episode, starring Matt Smith, David Tennant and John Hurt as the Doctor.
Billie Piper will return as Rose Tyler, while Jenna Coleman will continue as Clara Oswald.
The episode will also see the return of the Daleks and the Zygons.