Doctor Who will have a unique time travelling companion in the Christmas Special – in the shape of his first incarnation.

Harry Potter star David Bradley will reprise his role as the 1st Doctor, originally played by William Hartnell. Bradley previously portrayed the actor behind the first timelord for the BBC sci-fi show’s 50th drama An Adventure In Space and Time.

He will flank Peter Capaldi’s 12th Doctor in this year’s festive outing, following the departure of Pearl Mackie as Bill Potts at the end of this series (despite rave reviews after her debut on Saturday).

In the plot, the 1st Doctor has to help the 12th play out his last mission in the TARDIS. The pair must work together to save home planet Gallifrey by moving it to another dimension.

David Bradley playing William Hartnell's Doctor in 2013 (
Image:
BBC)

Fans will discover the close-up shot of Capaldi’s eyes from the 50th special, The Day of the Doctor, was actually the start of his own regeneration.

This series will be Capaldi's last (
Image:
BBC)

The scene, which was the only glimpse that viewers got of Matt Smith’s successor during the entire episode, will be returned to at Christmas as Capaldi transforms into the 13th Doctor.

12th Doctor cameo gave birth to #capaldeyes meme (
Image:
BBC)

Bradley, 73, is best known for his role as Argus Filch in the Potter films and as the suicidal newsagent in the first series of Broadchurch.

He first played Hartnell’s Doctor in drama-documentary An Adventure in Time and Space.

An insider revealed: “David was convincing as Hartnell, it’s exciting he’s back.

He will transform during the Christmas special (
Image:
BBC)
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“Four years ago it took all the previous Doctors to save Gallifrey, so maybe some of the others will also pop up in Capaldi’s swansong.

“It’s great that the 1st Doctor will be there to help out during those all-important regeneration moments.”

Hartnell, who died in 1975, played the 1st Doctor from 1963 to 1966.