We've now seen two of the three Doctor Who 60th-anniversary specials, but the next - titled "The Giggle" - will be the big one. So far, Donna's mind has been saved and she and the Fourteenth Doctor - who looks exactly like the Tenth - have embarked on another adventure together.
Next time, the Doctor and Donna will battle Neil Patrick Harris' Celestial Toymaker, and regardless of how it plays out, we know it will end with the hero's regenerating into Ncuti Gawta's fifteenth iteration of the Time Lord.
Spoilers that were posted before any of the specials aired have resurfaced today and, with the descriptions of "The Star Beast" and "Wild Blue Yonder" proven correct, it's safe to assume the breakdown of "The Giggle" is as well. As a result, we now know there's a huge twist coming which sets the stage for not one, but two Doctors moving forward.
Here's the leak in its entirety (apologies for the grammatical errors, but we're sharing it in its original form).
"The Toymaker says he has played one game with a previous doctor, the second with the Fourteenth now he must play with a next doctor. As the Fourteenth regenerates he finds he hasn’t changed but there is the Fifteenth Doctor next to him, this is where the 'What the hell is going on here' is said. Later they both in unison say 'I challenge you to a game!' the Toymaker annoyed says 'That’s cheating, there is 2 of you!' and Fourteen says 'But according to the rules you can’t say no.' he accepts the challenge."
"Together, they manage to win the game and The Fourteenth’s prize was to banish The Toymaker from existence. After the game, the Fourteenth Doctor, the Fifteenth Doctor, Donna, and Mel discuss the consequences of their adventures mentioning Sarah Jane, Adric, River Song. Donna tells the Doctors why don’t they just take a break and enjoy the simpler life. That’s when the Fifteenth Doctor remembers he hasn’t said what his prize would be. A second TARDIS! Now the Fourteenth Doctor stays behind while the Fifteenth flies off in his TARDIS."
There's clearly a fair bit of information missing here, but the gist is that we are indeed getting a "bi-regeneration," resulting in the Doctor splitting in two rather than leaving his old self behind. We have to believe this will lead to a spin-off revolving around David Tennant's Fourteenth Doctor, though some fans aren't happy with the decision.
They believe it makes Gatwa's Fifteenth Doctor little more than a "clone" and a stand-in for the real deal. That's not exactly fair when he'll be established as the Fifteenth Doctor; plus, we still don't know why this happens or what led to the Tenth Doctor's face returning (suggesting there's a much bigger story there).
Doctor Who showrunner Russell T Davies is likely playing the long game so we'll have to wait and see. This does, however, lay the groundwork for some very exciting future stories...