Capaldi will leave the show after the Christmas special episode when the Doctor regenerates.
The BBC sent fans into a frenzy when it released a trailer which hinted at the announcement of the new Doctor.
In the trailer, the TARDIS can be seen before the camera cuts to a key buzzing with electric energy.
The number 13 is then splashed across a mobile phone screen, number 10 Downing Street, the White Cliffs of Dover and The Statue of Liberty.
Capaldi recently revealed his regeneration sequence will be “more complicated than recent ones.”
Of leaving the show, the star told The Radio Times in June: “I can’t go into the details. I know what happens, but I don’t know how it happens.
“Certainly it’s not straightforward. It’s more complicated than recent ones