In an interview with Radio Times, Doctor Who BBC Centenary Special director Jamie Magnus Stone spoke of filming Jodie Whittaker’s thirteenth Doctor’s regeneration scene for the final of the three 2022 Doctor Who specials.

“I’m very fortunate in that I’m directing the last one of them. So I’m actually doing her regeneration.”

“Basically her last day of filming was most of the crew’s last day of filming as well. So it was all orchestrated to have this big, final last day. And we shot that last day for Jodie in story order. So we ended up on her last scene.”

“And we shot the last-ever scene in the TARDIS, and said goodbye to the TARDIS, and then there were some tears. And then we went out to film, basically, her regeneration. And the last shot that we did, I think, will be the last shot in the episode as well. So it was really nice to do things in sequence.”

So the regeneration scene was not filmed on the TARDIS interior set as so many regeneration scenes before it. This is likely why the TARDIS set at Roath Lock Studios in in Cardiff was in the process of being dismantled in November of 2021. The set will not be needed when the actor who portrays the next Doctor films the final part of the regeneration.

It’s unclear what Stone meant by “went out to film.” The most likely explanation is that the cast and crew exited the TARDIS interior set to film elsewhere inside Roath Lock Studios.

When Bad Wolf films the final part of the regeneration scene with the fourteenth Doctor actor, they will be based at Wolf Studios in Cardiff, not Roath Lock Studios. The easiest way to match Jodie Whittaker’s thirteenth Doctor regeneration footage with the regeneration footage of the actor playing the fourteenth Doctor is to not use a physical set at all. It’s possible the Roath Lock and Wolf Studios crews have and will use a green screen set as employed for the non-terrestrial Doctor Who: Flux scenes. The background footage for the actual regeneration location could then be added in post-production.

“It all worked out really nicely,” Stone further explained to Radio Times. “I think everything we shot that day is going to be absolutely lovely. Yeah, I can’t wait to show you guys.”

Written by Chris Chibnall and directed by Jamie Magnus Stone, The Doctor Who BBC Centenary Special will air in autumn of 2022.