This December’s Doctor Who Christmas special is set to be momentous for a number of reasons, with Twice Upon a Time serving simultaneously as Peter Capaldi’s final adventure as the Doctor, Steven Moffat’s final writing credit and Jodie Whittaker’s first appearance as the Thirteenth Doctor.

But of course the episode will also have the distinction of hosting the return of the very first incarnation of the Doctor, originally played by William Hartnell in the first 1960s episodes of the show and now taken over by David Bradley (after the Harry Potter and Game of Thrones star previously played Hartnell in 2013 making-of drama An Adventure in Space and Time).

And it’s the original Doctor’s inclusion that raises some of the most interesting possibilities about the upcoming episode. Since Bradley’s involvement was announced it’s been revealed that at least some of the action is taking place during Hartnell’s final episode The Tenth Planet, with the episode trailer depicting sets and characters from the episode.

Even more interestingly, the opening scene of the Twice Upon a Time trailer morphs between archive footage of Hartnell and new colourised footage of Bradley, leading many fans to wonder whether the finished episode will feature more recreations of the classic (and partially lost) episode – speculation only fanned by episode director Rachel Talalay in a recent interview.

“I feel like I’m an expert in the Tenth Planet! I think I’ve watched Tenth Planet more than anybody,” Talalay told the This Week in Time Travel podcast earlier this month when asked about her expertise classic-era Cybermen for the series 10 finale.

And then, she added an enticing postscript.

“Sections of it I’ve watched over and over again for reasons that will become clearer over Christmas,” she said.

“And also different reconstructions and the animated reconstructions. So yeah – I’ve watched sections of it a LOT.”

So could this suggest Talalay has been poring over these classic scenes so she can accurately recreate them just like Hartnell’s speech from the trailer? Will we see more morphs from the original episode to brand-new footage, or was that technique only intended for a one-off promotional shot? And generally speaking, will we spend this Christmas enjoying sections of the First Doctor’s final hours lovingly reimagined on screen, or watching a story that largely ignores the earlier one altogether?

Frustratingly as ever, we can’t know for sure until nearer the time. But we reckon old series fans like Moffat and Capaldi would be loth to miss out on the chance to pay tribute to a truly classic episode of Doctor Who – and even if they did go in a different direction, there are doubtlessly legions of fans who could stitch together the two stories for fleeting online acclaim.

One way or another, we’ll almost definitely see these two separate estranged figures brought together – and in the end, isn’t that what Christmas is all about?

Doctor Who returns to BBC1 this Christmas