Doctor Who
What's next for "Doctor Who" after the 50th anniversary special? BBC

While the “Doctor Who” 50th anniversary special, “The Day of the Doctor,” may be over, fans are still eagerly anticipating the show's Christmas Special. "The Time of the Doctor" will see Matt Smith's last performance as the Doctor as well as the introduction of Peter Capaldi as the Twelfth Doctor. As with all things "Doctor Who," the transition is not so straight forward as showrunner Steven Moffat added a bit of a wrinkle with comments made to the press.

The Time of the Doctor
"The Time of the Doctor" will air on Dec. 25. BBC

"The Time of the Doctor" will air on Dec. 25, on BBC One at 7:30 p.m. local time in the UK and on BBC America at 9 p.m. EST, 8 p.m. CST. BBC released a quick synopsis for the special stating, "Orbiting a quiet backwater planet, the massed forces of the universe’s deadliest species gather, drawn to a mysterious message that echoes out to the stars - and amongst them, the Doctor. Rescuing Clara from a family Christmas dinner, the Time Lord and his best friend must learn what this enigmatic signal means for his own fate and that of the universe."

Official photos reveal some familiar foes, including Daleks and Cybermen, and a new face, Tasha Lem, played by Orla Brady. While Lem's role in "The Time of the Doctor" is not quite clear, she is a woman from the Doctor's past, notes Metro UK. The teaser trailer indicates the Doctor will also face the Silence, wrapping up many of Smith's storylines prior to the introduction of a new doctor.

Tasha Lem
Tasha Lem's role in "The Time of the Doctor" has yet to be revealed. BBC

"The Time of the Doctor" wraps up a special year for "Doctor Who" fans and it will be interesting to see how Moffat handles the change. At a media briefing for "The Day of the Doctor," Moffat discussed the introduction of a new Doctor while also putting a unique spin on the numbering of the Doctors and what fans may expect from Capaldi's introduction.

"The Day of the Doctor" introduced a new Doctor, John Hurt, and a quick glimpse at the Twelfth Doctor, played by Capaldi. Hurt’s introduction as a Doctor means a shift in the numbering, with Matt Smith becoming the Twelfth Doctor and Capaldi to play the Thirteenth Doctor.

Aside from a numbering confusion, fans and experts note a central tenant of the “Doctor Who” mythology which adds another twist, and restriction to the regeneration process. As pointed out by Mark Jefferies, TV editor for the Daily Mirror, on Radio Times, Hurt is officially a Doctor. That would make Hurt’s Doctor the Ninth Doctor, following Paul McGann’s Eighth Doctor. For the new series, that would mean Christopher Eccleston is now the Tenth Doctor, David Tennant the Eleventh Doctor, Matt Smith the Twelfth Doctor and Peter Capaldi the Thirteenth.

The problem with that is “Doctor Who” mythology states there can only be 12 regenerations, meaning the show will be in tough spot at the end of Capaldi’s run as he would be the 13th incarnation of the Doctor. Jefferies says this restriction was established in 1976 in the episode “The Deadly Assassin.”

What’s worse is “Doctor Who” showrunner Moffat further complicating the matter. Speaking to Jefferies, Moffat says Smith is, technically the Thirteenth Doctor and Tennant used two regenerations. That would mean Moffat must find a way to explain Capaldi as the new Doctor, especially if wants to remain faithful to the ground rules that have been established in the series.

Of course, Moffat remained coy about what is going to happen during the Christmas special but fans can expected a more focused Doctor in the new season. At the end of “The Day of the Doctor,” Gallifrey has not been destroyed, instead being held in a pocket universe, which means the Doctor could, in theory, return home.

To hear more of Moffat’s thoughts on “Day of the Doctor” as well as the legacy and future of “Doctor Who” you can listen to his talk with the media, courtesy of Dan Martin, below.