The Doctors will return at Christmas
The cliff-hanger ending saw the Doctor fatally shot by a Mondasian Cyberman and begin to regenerate. Stepping out of the TARDIS into an arctic landscape, he fought off the glowing regeneration energy and fell to his knees, vowing that this time he would not live on and change into a new Doctor.
This was declared 'ridiculous' by an approaching figure, who mocked the Doctor as he stepped forward through the snow to reveal himself as the very first incarnation of the Time Lord ("The original, you might say") just before the credits rolled. The story will continue at Christmas.
Further casting and details for the Doctor Who Christmas special will be revealed in due course. As previously announced, the special will serve as Peter Capaldi's farewell to the series, and will feature the debut of the next Doctor.
Pictured: The Doctor (Peter Capaldi) and the First Doctor (David Bradley)