With the Doctor Who 50th Anniversary now a thing of the past, the BBC show is gearing up for the Eleventh Doctor's final performance in the Christmas Special.

Set to regenerate in the upcoming holiday episode, Matt Smith (Eleventh Doctor) will relinquish his Time Lord role to Peter Capaldi. Unfortunately, the events of the 50th Anniversary have put a few kinks into the supposed timeline of events.

Whovians now know that John Hurt's Doctor can be counted as a regeneration, bringing the total number of Doctors to 12. This is significant because a 12-regeneration cap (which allows for 13 iterations of the Doctor) was previously instituted in the 1976 episode "The Deadly Assassin" and this rule would need to be altered if the series wants to continue past Capaldi.

However, if Ten's (David Tennant) botched regeneration - which resulted in his half-human doppelganger - also counted as a regeneration, then this rule would need to be fix before Eleven bites the dust.

"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," said executive producer Steven Moffat, according to the Radio Times.

"So if the Doctor can never change again, what's Peter Capaldi doing in the Christmas special?"

To make matters even more complicated, a new preview for the Christmas Special makes it look as if Eleven will be somehow revisiting the mystery of Trenzalore, also known as the gravesite of the Doctor. According to the Radio Times, the episode will include a speech by Eleven regarding the topic of death.

With all these snippets of information blowing around, Whovains have been left scratching their heads in confusion. How exactly will Capaldi's Doctor come into play?

To find out how the Doctor Who manages to sort out this plot tangle, tune in for the Christmas Special on Dec. 25.

Tags: Doctor Who BBC television