Doctor Who Peter Capaldi David Bradley
A promotional shot for Twice Upon a Time featuring Capaldi and Bradley. BBC

Doctor Who's Christmas Special will feature Peter Capaldi's Twelfth Doctor and David Bradley's First Doctor bickering over the latter's old-fashioned chauvinism, it has been revealed. The pair will star in the what will be writer Steven Moffat's final episode as showrunner.

Bradley, best known for his role as Filch in the Harry Potter films, will take on the role originally played by William Hartnell in the 60s, having played the actor in 2013 docudrama An Adventure in Space and Time, which was about how the iconic BBC show made it to the screen.

The 75-year-old actor appeared at the end of the finale of Doctor Who's latest season, playing the first Doctor in a canonical episode for the first time and setting up this year's festive special.

Capaldi and Bradley will team up this Christmas in Twice Upon a Time, in a story that will see the two Doctors time-travel to the First World War.

As is sometimes the case when two Doctors meet however, they don't exactly get on fantastically well.

"What we did emphasise," Bradley explained at the London Film & Comic Con (via Den of Geek), "was the old fashioned nature [of the character] and how he is from the 60s.

"He goes into the Twelfth Doctor's Tardis and says 'it's a bit dusty around here, it's in an awful state isn't it? Where's Polly? Shouldn't she give it a spring clean?' And then Peter's saying 'you can't say that'."

Bradley goes on to say that the First Doctor "brings all his 60s sensibilities, what's lovingly called casual chauvinism.

"He's just talking [as if] the [companions] are there just to help out, and do the dusting and do all the domestic chores – his attitudes to a lot of things come right from the 60s, so there's a lot of conflict between Hartnell's Doctor and Peter's Doctor about how things have changed in the last 50 years... we had quite a bit of fun with that."

Twice Upon a Time will be Capaldi's final appearance as the Doctor as well as Moffat's swansong as showrunner. This year's tenth season (of the rebooted version of the show) finished with Capaldi stubbornly putting off his regeneration.

When he does regenerate in the Christmas Special, the character will become a woman for the very first time. In July it was revealed that Broadchurch star Jodie Whittaker will play the Thirteenth Doctor in season eleven next year.

Whittaker will likely make here debut in the Christmas Special when it airs this Christmas Day on BBC One.