The new Doctor Who will be unveiled in a live television special on Sunday.
The identity of the next Time Lord has been a closely-guarded secret - BBC executives have been using the codeword "Houdini" to stop it getting out.
Matt Smith, who has played the role since 2010, will bow out in the Christmas special and be replaced by the latest incarnation of the Doctor.
Zoe Ball will present this Sunday's special reveal show at 7pm on BBC1, which will feature interviews with Smith and executive producer Steven Moffat, among others.
Mr Moffat said, "The decision is made and the time has come to reveal who's taking over the Tardis. For the last of the Time Lords, the clock is striking 12."
BBC drama controller Ben Stephenson said he cannot wait to unveil the next Doctor Who live on TV.
"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," he added.