It was Peter Capaldi’s idea to bring David Bradley back to play the First Doctor in Twice Upon A Time!
Bradley has been a part of Doctor Who since 2012, when he appeared in Dinosaurs on a Spaceship as Solomon the trader; the following year, he played William Hartnell in the 50th anniversary docudrama, An Adventure in Space and Time – but this Christmas, he returns to Doctor Who, this time as the First Doctor. As outgoing showrunner, Steven Moffat explained:

“I was at New York Comic Con and someone was asking me about the War Doctor in The Day of the Doctor – I was talking about maybe the biggest contrast you could have between Doctors, because they are all the same person and obviously there is a limitation.

“I said, ‘Well the ideal one you want to do is William Hartnell meets the current Doctor, because that’s such a colossal difference; he’s so different by that stage. Imagine how that lovely sweet old man, who isn’t the least bit crotchety when you go back and look at him, would react to discovering he’s this buccaneering space hero with the ego the size of a planet. How’s he going to react? What’s he going to say? But we can’t do it because William Hartnell’s dead.’

“Peter [Capaldi] said ‘We can get David Bradley,’ and I thought ‘Oh yeah, actually we could. We could absolutely do that.’ So we did.”

Bradley debuted as the First Doctor in the cliffhanger to The Doctor Falls, which leads directly into this year’s festive special.
The Broadchurch actor did an incredible job as Hartnell in An Adventure in Space and Time, but I feel like his role, this recasting, might prove massively divisive. Despite Richard Hurndall playing the first incarnation of the Time Lord in The Five Doctors, to some, it still feels wrong to recast important cast members. But I guess we shall see!
Twice Upon A Time airs on BBC1 on Christmas Day 2017 at 5:30pm.