In the last Doctor Who 60th anniversary special, The Giggle, the Fourteenth Doctor split like an amoeba into two separate Doctors. Thus Ncuti Gatwa’s Fifteenth Doctor came into existence while David Tennant’s Fourteenth remained.

For all of previous Doctor Who history, the regeneration is a complete transition from one Doctor the another. The former Doctor doesn’t survive the process — until now.

One might assume this is a one-off but, in his iPlayer in-view commentary for the special, Doctor Who showrunner Russell T Davies explained to Tenth Doctor actor David Tennant and producer Phil Collinson that bi-generation has now occurred throughout the Doctor’s timeline — which means it is also likely the case going forward.

“So then, so a whole timeline bi-generated then. So Sylvester McCoy[‘s Doctor] woke up in a drawer in a morgue in San Francisco… And Jon Pertwee[‘s Doctor] woke up on the floor of the laboratory. They all did.”

“Most of those, the modern Doctors, just end up in their own TARDIS. So Peter Capaldi[‘s Doctor] just woke up in the TARDIS. You, (speaking to David Tennant), your tenth version, still also out there, just woke up in the TARDIS.”

This is the most significant change to Doctor Who lore ever conceived. The mind boggles. When I first heard of this, I thought, ‘Big Finish (audio adventures) is going to have a field day with this.’ Every Doctor, everywhere, all the time.

Regeneration has always occurred when the Doctor is mortally wounded or has aged to end of their conceivable existence. It is the Doctor’s way of cheating death by living on in a different body — recast to a new actor.

When it comes time for the Fifteenth Doctor to regenerate, he may also bi-generate instead. This effectively eliminates the pathos of the regenerative process. No Doctor needs fear the end of their unique existence from now on. One wonders how the salient drama formerly endemic to the process will be sustained.

But this is not a dilemma for fans to solve. It’s up to Russell T Davies to provide the requisite drama.

Ncuti Gatwa’s first full episode as the Doctor, The Church on Ruby Road, will be available on 25 December exclusively on BBC One and BBC iPlayer in the UK and Ireland at 5:55pm BT and streams on Disney+ globally outside of the UK and Ireland.

A new 8-episode Doctor Who series starring Ncuti Gatwa and Millie Gibson will debut in Spring of 2024 followed by the 2024 festive special later in the year.