In an interview with the Radio Times, Moffat said: “We’ll find out that Matt Smith is actually the 13th Doctor. Although everyone knows that the Doctor can only regenerate 12 times.”
“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?”
The Christmas Special, ‘The Time of the Doctor’ will air on Christmas Day at 7:30pm on BBC One.