This article contains spoilers for Doctor Who's Centenary Special, The Power Of The Doctor.The Doctor Who Centenary Special, The Power of the Doctor, ended with Jodie Whittaker's Thirteenth Doctor unexpectedly regenerating into David Tennant. Jodie Whittaker's time as the Thirteenth Doctor has come to an end. For the first time, though, viewers approached a regeneration scene with no real idea what to expect; although Ncuti Gatwa has been cast as the next Doctor, David Tennant is mysteriously returning for Doctor Who's 60th anniversary in 2023. This, naturally, led to intense debate over whether Whittaker would regenerate into Tennant or Gatwa.
In the end, Jodie Whittaker regenerated back into David Tennant. In a delightful homage to Tennant's debut as the Tenth Doctor, this new incarnation of the Doctor was taken aback to realize he recognized these teeth. This was quite clearly the last thing the Doctor had expected - the brief scene ended with Tennant issuing his iconic triple-"What?" - but it isn't too surprising to see something go wrong with this particular regeneration. The Master had tried to steal the Doctor's infinite regenerations through a so-called "forced regeneration," so it's entirely understandable that the Doctor's next regeneration - coming so soon after - would be disrupted.
Something Has Gone Badly Wrong With The Doctor's Regeneration
Although many Time Lords have precise control over their regenerations, for the Doctor it's always been something of a lottery. That's largely because the circumstances of the Doctor's regenerations are typically the result of trauma, rather than simply a body "wearing a bit thin." To date, the most traumatic regeneration was Peter Davison's transformation into Colin Baker, with the Doctor coming within a hair's breadth of actual death; Baker's Sixth Doctor was dangerously unstable, even attempting to throttle his companion.
The Power of the Doctor was accompanied by a brief trailer for Doctor Who's 60th anniversary specials, and it appeared to confirm Tennant's new Doctor will struggle to maintain any real sense of identity. This could explain why Tennant's new Doctor seeks out Catherine Tate's Donna Noble - wanting help to ground himself. The trailer also offered a glimpse of Gatwa, frustrated, calling out: "Will someone tell me what the hell is going on here?" All this suggests the Thirteenth Doctor's regeneration really has misfired.
The Thirteenth Doctor's Regeneration Could Have Been Affected By Outside Forces
There is, however, one major clue to what's going on in the Thirteenth Doctor's regeneration; the fact her clothes changed. This is particularly surprising, because a Time Lord's clothes don't normally change when they regenerate. There's no way even a failed regeneration can affect the Doctor's clothing like this, although it's interesting to note the transition did involve the same kind of temporal energy flare that accompanies a regeneration. Still, the clothes perhaps imply an alien force has interfered with the regeneration - and the 60th anniversary special features Neil Patrick Harris as the Celestial Toymaker, a cosmic entity who could well be the culprit.
Everything is theory at this point, of course. What is certain is that Doctor Who has just done something that has never been done before; the Doctor has de-generated, taking on a form they had possessed in the past. The Power of the Doctor launches the era of returning showrunner Russell T. Davies in style, promising to build on the past while setting up the future. Hopefully it won't be long before the BBC confirm just when the next Doctor Who episode will air as part of the 2023 celebrations.