Doctor Who’s series 10 finale paid tribute to the sci-fi show’s history with appearances from some of its former stars, giving a sneak preview of the Christmas special.

The episode, entitled The Doctor Falls, was Peter Capaldi’s penultimate in the starring role and saw the beginning of the end of his incarnation as the 12th Doctor.

In last week’s episode, companion Bill (Pearl Mackie) was turned into a Cyberman.

Saturday’s instalment saw the Time Lord battle against the growing swarm of Cybermen as his enemies Missy (Michelle Gomez) and the Master (John Simm) delighted in his horror at the prospect of his own regeneration.

Doctor Who
The Doctor came face to face with the Doctor (BBC)

As the Doctor’s regeneration process began, viewers saw his flashback through previous incarnations as past sidekicks played by Billie Piper, Jenna Coleman, Catherine Tate and John Barrowman were seen calling out his name.

But the biggest clue to the plot of this year’s Christmas special came in the closing moments of the episode when Capaldi’s character struggled outside of the Tardis into a snowy wasteland and came face to face with the original Doctor.

The 12th Doctor shouted: “I don’t want to change again, never again, I can’t keep on being somebody else.

Doctor Who
Peter Capaldi and David Bradley starred together (BBC)

“I’m staying. I will not change. I am the Doctor.”

But he was answered by a figure who emerged through the snow saying: “No, no, no, I am the Doctor, the original.”

Played by David Bradley, the character was dressed as the late William Hartnell’s Doctor, the first ever incarnation of the Time Lord.

Doctor Who
Bill said a tearful goodbye to the Doctor (BBC)

It harked back to a 1966 episode, The Tenth Planet, in which the Doctor travelled to the South Pole to take on the Cybermen.

Fans tweeted about how impressed they were with the finale, also marking the end of writer Steven Moffat’s time at the helm of the series.

However, there was some disappointment at still not knowing who Capaldi’s successor would be.

Elsewhere in Saturday’s episode, Gomez bowed out as Missy was shot by the Master and Bill’s love interest from her debut episode, who disappeared as a ghost in a watery puddle, returned to invite a grieving Bill to travel through the universe by her side.

Capaldi will return for a final appearance in the Doctor Who Christmas special.