Warning: Spoilers for Doctor Who's finale, "The Doctor Falls," are in play. If you're not current with that most recent episode, feel free to come back once you've enjoyed it.
Throughout Season 10's plotline, Doctor Who has hinted at the eventual real-world departure of the current actor in the titular role, Peter Capaldi. With the world watching and waiting for the announcement and reveal of a brand new Doctor, most thought the season finale was an obvious target for the unveiling. However, by the time the finale "The Doctor Falls" wrapped up the season's story, we were left without a new Doctor to take Capaldi's place. As previous rumors had hinted at, though, the "First Doctor" returned for an excellent lead-in for the Christmas special.
The last moments of the season finale saw The Strain's David Bradley return to the First Doctor role that William Hartnell originated, after previously portraying him in the TV biopic, An Adventure in Space and Time. Strangely enough, it looks like that the First Doctor will be going through a crisis of his own when it comes to his image, which is the perfect parallel for Peter Capaldi's Doctor, as he is also deferring the big change due to his headstrong nature. So, for everyone hoping to see a new Doctor in the mix, you got your wish...just probably not in the most expected way, and now we'll definitely be waiting another six months or so to see Thirteen appear in the flesh.
Of course, that grand reemergence came after The Doctor defiantly proclaimed that his regeneration just wasn't going to happen. Sacrificing himself to defeat the Cybermen, The Doctor blew up an entire floor of the ship that he, Bill, and Nardole found themselves on, and naturally "killed" himself in the process. So fed up with the prospect of changing into another person, he defiantly fought the status quo, and he's been successful so far, by all counts. Who'd have thought shoving one's hands into a snowbank and yelling really hard about it could stop one's physical appearance from shifting?
Just as Steven Moffat had been promising, the Doctor's regeneration is going to be anything but typical this time around. Although, to be fair, David Tennant and Matt Smith both had moments where they manipulated their regenerations to a certain extent. Still, Peter Capaldi will have (and has earned) his own unique exit, as he'll eventually have to walk that path all good Time Lords have tread before him.
Seeing as Steven Moffat hasn't been shy in former seasons about using past Doctors to help usher in the new kid on the block, many speculated that Peter Capaldi's Doctor would merely return for a cameo to help the new addition's tenure kick off. That's exactly what Matt Smith did in "Deep Breath," which started off the Capaldi era with flying colors for Season 8. But instead, the Christmas special has become the traditional regeneration episode for Doctor Who. Gone are the days of the Ninth Doctor, where the character would regenerate at the end of their final season, only to become a new person in time for Christmas.
We're already sad enough to have seen Bill Potts reunited with Heather, as a sort of celestial entity similar to The Pilot that took Heather's form; so if anything, it was nice to see that we can save some tears for a Christmas regeneration. But with Peter Capaldi's rage against his growing light, we saw a most devastating pre-regeneration sequence setting up a familiar theme: the acceptance of change. While there's still time on the clock for the Twelfth Doctor, we all know the big day will be here sooner than later. It's never a matter of if The Doctor will regenerate, but a question of how we'll be lead down the path of acceptance.