This article contains spoilers for the Doctor Who Centenary Special, The Power of the Doctor.David Tennant’s return to Doctor Who hints at a link to Tom Baker’s abandoned movie-length anniversary special from 1993. « The Power of the Doctor » ended with Jodie Whittaker regenerating into David Tennant, which sets the actor up as both the Tenth and Fourteenth Doctors. However, the way that David Tennant plays the realization suggests that the Doctor is horrified to be back in the body of the Tenth Doctor again, hinting at a larger mystery in 2023’s 60th anniversary specials.
It’s already known that Ncuti Gatwa will be taking over from David Tennant at some point in Doctor Who’s 60th anniversary specials. A brief trailer released after « The Power of the Doctor » aired revealed the first look at Ncuti’s Doctor, dressed in Tennant’s shirt and tie, frustratedly asking: « Can someone tell me what the hell is going on here? » This further suggests that the Thirteenth Doctor’s regeneration into the body of the Tenth Doctor is a problem to be solved in the specials. If someone has altered the past to bring back Tennant’s Doctor, then it would be a similar plot to Lost in the Dark Dimension, the abandoned 30th-anniversary movie from 1993.
Originally intended as a straight-to-video movie for the 30th anniversary, The Dark Dimension was written by Adrian Rigelsford and would be directed by stalwart Doctor Who director Graeme Harper. The project was sparked by Tom Baker’s desire to return to the role of the Doctor. It had been over a decade since Baker had last played the Doctor, so a script was written that depicted an alternate dystopian world where the Fourth Doctor’s death had been averted by a nefarious villain.
This meant that the Fifth, Sixth, and Seventh Doctors were erased from time and it was down to Ace (Sophie Aldred) and the Brigadier (Nicholas Courtney) to help the Doctor put things right and set time back on the right course. The end of the film would have seen the Seventh Doctor heading off on new adventures, but a combination of behind-the-scenes issues led to the project being abandoned. Interestingly, one early draft of the script saw the Doctor collapse in the TARDIS at the end, potentially signaling a new Doctor. Given that Ncuti Gatwa is set to take over from David Tennant, it seems the former Tenth Doctor is playing a similar role to Tom Baker’s Fourth Doctor.
Not much is known about the plot of Doctor Who’s 60th anniversary, which is understandable given that it’s not due to air in 2023. However, the Doctor’s identity crisis, and RTD’s mention of puppets does draw parallels with the way that the Fourth Doctor was manipulated by the villain of Rigelsford’s Dark Dimension. In the same statement, RTD names Ncuti Gatwa as the 15th Doctor, but while the article states that Tennant is the 14th Doctor, Davies doesn’t actually explicitly state this: « If you thought the appearance of David Tennant was a shock, we’ve got plenty more surprises on the way! » (via Doctor Who)
RTD’s quote about surprises, and the fact that the Doctor’s clothes changed during their regeneration suggests there’s more to Tennant’s return than it appears. The Doctor’s clothes have changed before during regeneration, most notably when the First Doctor turned into the Second. It’s since been speculated that the clothes changed because the TARDIS stepped in to assist the Doctor’s regeneration. It is possible that someone else has interfered with the Thirteenth Doctor’s regeneration, or as in The Dark Dimension, their timeline, which has left the Tenth Doctor standing on the cliff rather than a post-regeneration Fourteenth. Doctor Who fans will find out the truth in November 2023.