When Matt Smith’s Time Lord regenerates during the upcoming Doctor Who Xmas episode, Peter Capaldi will become Doctor number Twelve. Or will he?

As all Doctor Who fans know, the Doctor can—technically—only regenerate 12 times; something that Who showrunner Steven Moffat recently confirmed.

That’s all mighty fine and dandy, but the trouble is that we’re getting pretty darn close to that regeneration limit.

Not so fast! According to Moffat, there’s something we’ve all missed.

Talking to Radio Times, the Doctor Who showrunner said:

“He can only regenerate 12 times”, while simultaneously suggesting there has been a miscalculation of how many regenerations he has actually been through.

“I think you should go back to your DVDs and count correctly this time," said Moffat, "there’s something you’ve all missed.”

What did we all miss, then?

Sure, the Tenth Doctor once used all his regenerative energy and channeled it into his severed hand, thus giving us the metacrisis Doctor ("The Stolen Earth" and "Journey's End") as well as keeping David Tennant on as the Doctor for a couple of specials before leading the way for Matt Smith’s Eleventh Time Lord.

There's also the fact that we never saw the Eighth (Paul McGann) Doctor’s regeneration into Nine (Christopher Eccleston). And where does that leave John Hurt’s mysterious Doctor, first and last seen at the end of "The Name of the Doctor"? Hopefully, we'll get our answers about him in the upcoming 50th-anniversary special, "The Day of the Doctor."

Also, and this bears thinking, we had River Song (Alex Kingston) give up all her own regenerative energy (she regenerated two times that we know of) to Matt Smith’s Doctor as he lay dying in "Let's Kill Hitler." For realsies. Could this have been used by Steven Moffat as a way to reset the number of times the Doctor can regenerate or has regenerated?

What do you think we’ve all missed?

(via Radio Times)