Theories behind David Tennant's Doctor Who regeneration costume twist

As had long been rumoured, the Time Lord did not regenerate into the version that will be played by incoming star Ncuti Gatwa, but instead to a previous iteration – the one played by David Tennant.

But that wasn't the only odd thing about this regeneration. As thousands of viewers were quick to point out, the Doctor's outfit also changed, which is a major departure from the usual way of things.

So, what exactly is going on here? Read on for everything you need to know.

Doctor Who's regeneration outfit change explained

The first thing to note is that although this regeneration anomaly is certainly unusual, it's not entirely without precedent on the show.

The very first regeneration – when William Hartnell was replaced by Patrick Troughton – also saw the new Doctor wearing an entirely different outfit straightaway.

That said, the show was still very much in its infancy at that point in its run, and the exact rules of regeneration had not been fully established. In this instance, the sudden break from tradition seems all the more noteworthy.

Indeed, the episode itself even made it clear that the Doctor's clothes should not regenerate along with her, with a key plot point seeing The Master forcing a regeneration and ending up wearing the Thirteenth Doctor's familiar outfit.

And so it seems pretty certain that this is not a simple continuity error but rather a deliberate choice that could offer some clues as to what lies ahead in the future.

What exactly it might be hinting at is far less certain, but it seems very clear that something has gone terribly awry with this regeneration – and the most obvious interpretation is that some kind of external source is adversely affecting things.

That external source could well be the Celestial Toymaker, a classic villain who has already been confirmed as the main antagonist for next year's 60th-anniversary celebrations – with Neil Patrick Harris set to take on the role.

In all likelihood, the Celestial Toymaker is responsible for the unusual regeneration – but as for the specifics on how things have exactly gone wrong, we'll have to wait until next year to find out...

Read more about Doctor Who:

• Doctor Who's Mandip Gill "wouldn't have wanted it to end any other way"
• Jodie Whittaker, Mandip Gill open to Doctor Who returns after exit
• Jodie Whittaker’s final words in Doctor Who were changed at last minute
• Doctor Who's Sacha Dhawan: 'I'll never, ever forget playing the Master'
• Doctor Who’s Sacha Dhawan “overwhelmed” at getting to play the Doctor
• Doctor Who’s Sacha Dhawan would “love to come back” to face Ncuti Gatwa

Doctor Who is available to stream on BBC iPlayer with episodes of the classic series also available on BritBox – you can sign up for a 7-day free trial here. Check out more of our Sci-Fi coverage or visit our TV Guide to see what's on tonight.

The latest issue of Radio Times magazine is on sale now – subscribe now and get the next 12 issues for only £1. For more from the biggest stars in TV, listen to the Radio Times View From My Sofa podcast.