[caption id="attachment_143903" align="aligncenter" width="1280"] 'The Time of the Doctor' (Photo: BBC)[/caption]

Regeneration stories are always special in Doctor Who. And this counts double for a regeneration story that both acknowledges the rules as set down by previous generations of scriptwriters, and then goes on to add new layers of folklore for future fans (and showrunners) to puzzle away at.

So amid all of the debate over which of the Doctor's regenerations we have reached, and whether he must die at the end of this incarnation, we find out exactly how elastic Time Lord science and physiognomy can be, discover that the Doctor did indeed manage to save Gallifrey somewhere, and get to see a wooden Cyberman.

Here's BBC AMERICA's recap of the story, and assuming we're all caught up with everything, here are your 10 facts:

1. It's probably not that big of a surprise to note this, but this story takes place over a longer time period in the Doctor's life than any other, as he ages 900 years while defending Trenzalore. "Utopia" sees the Doctor travel over a greater span of time, but it's a blink of an eye as far as the TARDIS travelers are concerned. "The Time of the Doctor" is also the shortest regeneration tale of all the televised serials. "The Night of the Doctor," while only 7 minutes long, was not intended for conventional broadcasts.

2. The original plan was to call the story "Twelfth Night" as a seasonal reference and pun on the arrival of Peter Capaldi as the Twelfth Doctor. But as it had been preceded by "The Name of the Doctor," "The Night of the Doctor" and "The Day of the Doctor," it was felt the title "The Time of the Doctor" would complete the series more fittingly.

[caption id="attachment_143943" align="aligncenter" width="1280"] Matt Smith in 'The Time of the Doctor' (Photo: BBC)[/caption]

3. When the Doctor has to try and translate the messages coming from the crack in the wall on Trenzalore, he uses the Seal of the High Council of the Time Lords, saying that he stole it from the Master in the Death Zone. This is a reference to "The Five Doctors," the 20th anniversary special, in which four of the Doctor's first five incarnations (and several of their companions) are whisked into a gladitorial arena on Gallifrey with various Daleks, Cybermen and the Master.

4. Clara's gran is played by Sheila Reid, her second appearance on Doctor Who. She originally appeared in the 1985 Sixth Doctor adventure "Vengeance on Varos" as a character called Etta. She would later reappear in the Twelfth Doctor story "Dark Water," once again as Clara's gran.

[caption id="attachment_143912" align="aligncenter" width="1280"] Sheila Reid as Clara's gran and Etta (Photos: BBC)[/caption]

5. And she's not the only one sitting around the Oswald's festive table with previous Doctor Who experience. Elizabeth Rider, who plays Clara's dad's girlfriend Linda, was also the voice of Atmos, the malevolent sat-nav in "The Sontaran Stratagem."

6. As Matt Smith had shaved his head for his role in the movie Lost River, and Karen Gillan had shaved her head for her role in Guardians of the Galaxy, the scene at the very end in which the Doctor hallucinates the return of Amy Pond to come and say "Raggedy man, good night" is notable for being the only time in Doctor Who history when the two principal actors are wearing wigs in order to look like themselves with their real hair (as opposed to the normal extensive hair and makeup to make people look like aliens). Steven Moffatt wrote a reference to Matt's haircut into the script, but as the Doctor was supposed to have no hair whatsoever (and a wig to hide his TARDIS key in), Matt had to wear a latex bald cap.

7. Not only had Matt had a haircut, he injured his knee during the early days of production and required an operation. This lead to the rumor of a script rewrite—later to surface for real in the the short story collection Tales of Trenzalore—that suggested that the Doctor had lost a leg to a Weeping Angel during his long vigil defending the planet. Matt's injury did lend a certain verisimilitude to those scenes where the aged Doctor walks with a stick.

8. The voice that comes through the crack, asking "Doctor who?" repeatedly, is that of Ken Bones, who played the Time Lord General in "The Day of the Doctor" who had to sign off on the Doctor's plan to hide Gallifrey.

9. During the first read-through of the scene where the Doctor regenerates, Matt Smith—at pains to point out that he's not normally a "weepy guy" in the episode's Behind the Lens special—had a bit of a tearful moment when he reached the line "I will not forget one line of this, not one day, I swear. I will always remember when the Doctor was me." Steven Moffat had to go over and give him a hug.

10. One of the original plans for the regeneration was that the Doctor's closest friends during his eleventh incarnation would revisit him, just as the Fifth Doctor's companions returned to him during his transformation. There would be Amy and Rory and Rory's dad Brian, River Song, the Paternoster Gang and Craig and Sophie Owens with baby Alfie (Stormageddon). Then there was a revised plan that Handles and Barnable—the Doctor's companions on Trenzalore—would make one last appearance. In the end, a final visit from Amy was all the Doctor needed.

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