It’s been, what, 36 hours since “The Day of the Doctor” finished, and already debate is starting to build up over what the inclusion of John Hurt’s War Doctor will mean in terms of the regeneration rules.

In case you have only a passing interest, it’s been a staple of Doctor Who that Time Lords are only given the ability to regenerate 12 times, giving 13 possible incarnations. This was first stated in the 1976 story “The Deadly Assassin,” in relation to the Master, but as time has gone by, it’s becoming a more pressing issue for the continuation of the show.

Although it was thought that we had at least one last regeneration after the Eleventh becomes the Twelfth Doctor on Christmas Day. However, Steven Moffat has now revealed that this is not the case.

Speaking to the Daily Mirror, he pointed out that the Metacrisis Doctor (generated when the Tenth Doctor was shot by a Dalek and he diverted the excess regeneration energy into his own severed hand) counts as one regeneration, and now so does the War Doctor.

So the Eleventh Doctor is now the Thirteenth Doctor (despite what Mr Moffat may have previously clamed). And Peter Capaldi is lined up to play a man who cannot exist.

Or, as Steven himself has put it: “The 12 regenerations limit is a central part of Doctor Who mythology – science fiction is all about rules, you can’t just casually break them.

“So if the Doctor can never change again, what’s Peter Capaldi doing in the Christmas special?”

Naturally, he offers no reply to this question, nor should we expect one until…ooh, December 25?

And yes, we welcome your theories below…

See more:

Steven Moffat: “Matt Smith Is Still The Eleventh Doctor”

‘Doctor Who’: A Companion To The Eleventh Doctor

Best of ‘Doctor Who’ 50th Anniversary Poll: Top 5 Doctors

‘Doctor Who’: Steven Moffat Explains Billie Piper’s Role in the 50th