The annual Doctor Who Christmas Special is always a TV highlight, even more so than when there's a regeneration looming. This year's offering, "Twice Upon a Time," not only saw the departure of Peter Capaldi as the twelfth Doctor, but also Steven Moffat as showrunner. The special also stood out for one very major change; the incoming Doctor is a woman.The brief but fabulously fun appearance of Jodie Whittaker aside, Capaldi's last episode of Doctor Who was poignant and filled with emotion. It also featured David Bradley as the first Doctor, who like the twelfth was trying to resist regeneration. We've seen this before, of course; David Tennant's Doctor was very anxious not to go, and Matt Smith's wasn't too happy about it, either. But Capaldi was actively trying to prevent the process from happening, and he successfully managed to delay it for quite some time before accepting the inevitable.Related: Doctor Who Christmas Special Review: The Series Embraces ChangeRegeneration started for Twelve at the end of Season 10 (after taking out the Cybermen), and he stated outright that he didn't want to change. Bill had been taken from him, Nardole was living on another planet, and the Doctor was alone and hurting. Yet, he still wanted to stay. That shows, as had often been the case during Season 10, that there is a human, more emotive side to the Doctor. He's alien, yes, but he's capable of feeling worried, scared, and apprehensive just like the rest of us.The Doctor Actually Could Have Died (This Page)

The Doctor Actually Could Have Died - If He Chose It

So we know the current Doctor doesn't want to go, and neither does (or did) the First, but Twelve can't remember this fact, which seems strange. It's, of course, to maintain continuity, but does have some in-universe basing. While the Doctor certainly does remember things, events, and people from his past, he seemingly cannot recall meeting future incarnations of himself; it's set up in "The Day of the Doctor," when Eleven confirms that John Hurt's War Doctor won't remember the truth of his actions. So, if the first Doctor won't remember meeting Twelve, does that mean that Twelve has forgotten what it was like to be One?

No matter the science (or timey-wimey) behind all that, both men come to find some common ground. œWe have a choice, either we change and go on, or we die as we are, Twelve tells One, and we know, of course, what choice both versions will make. This isn't a clear-cut aspect, though; the Doctor has already confirmed (in Season 9) that if a Time Lord is injured badly, they will die instead of regenerate, so death can come to the Doctor and maybe, one day, it will. For now, though, there's a regeneration on the cards.

Still, bearing in mind that death is something that can happen, it's fairly ominous that just before Capaldi gives his regeneration speech, he 'replies' to the TARDIS with "I suppose one more lifetime won't kill anyone. Well, except me." Is that a clue of what's to come in the future? For one of the longest running TV series of all time, it seems doubtful for now, at least. However, Capaldi's final speech, directed to his incoming replacement, does contain several references to Doctor Who lore, including a nice nod to Capaldi himself, who has always been a lifelong Doctor Who fan.

Doctor Who Twice Upon a Time

The Meaning of Capaldi's Final Words

That's not the sum of Capaldi's regeneration, though, with a final speech that rounds off his tenure in fitting fashion - complete with plenty of Who references and callbacks.

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"Never be cruel, never be cowardly," was first said on screen during "The Day of the Doctor," when Ten and the War Doctor told Clara it was a promise they'd once made. Capaldi's Doctor has earned quite the reputation for delivering powerful, impassioned speeches during his tenure, and one can certainly never accuse him of being cowardly, or cruel. These opening lines really hit home, because they are so obviously words that he's lived by. Of course, this being Doctor Who, we quickly move into amusement, when he follows his initial lines with "And never eat pears!" It's delivered with a sense of importance, and although it's funny, it's also very sad; he told the same thing to Clara just before he lost his memories of her, and told her to write it down.

"Remember, hate is always foolish, and love is always wise. Always try to be nice and never fail to be kind." Again, these words are ones that the Doctor has always preached; in "The Zygon Inversion," Capaldi gave one of the Doctor's best speeches ever, dissecting war and he drawing attention to how futile it is to hate, on both sides. From there, the Doctor addressed the subject of his name, with the following lines:

"You mustn't tell anyone your name. No-one would understand it anyway. Except¦. Except children. Children can hear it. Sometimes if their hearts are in the right place, and the stars are too. Children can hear your name."

The outgoing Moffat wrote these lines specifically as a personal goodbye to Capaldi; they're lines that Capaldi himself spoke at the screening for season 10, when a child in the audience asked about the Doctor's real name:

œI don't think human beings could even really say his name," he told the kid. "But I think we might be able to hear it. At a certain frequency. If the stars are in the right place, and your heart's in the right place, you'll hear it,

Related: Doctor Who's Christmas Special Wasted Its Two Doctors

This earned a huge round of applause at the screening, and really is an answer that only a dedicated fan of the show could give; Capaldi's passion for Doctor Who and his appreciation of the role has always been clear, and so when it came time to write his final lines, Moffat remembered this and wrote it in.

Jodie Whittaker Doctor Who

Reminding his new self to "Laugh hard, run fast," and "be kind," Capaldi's final words were "Doctor, I let you go," a decision that hadn't been easy, but that was necessary for Twelve to make.

With that, a new Doctor appeared and, catching sight of herself in the TARDIS screen, uttered her first words; "Oh, brilliant," in a broad Yorkshire accent before accidentally spinning the TARDIS out of control and falling into outer space. How will the Doctor correct her course? Well, we have to wait until Fall 2018 to find out. Saying goodbye to Capaldi's Doctor was tough, but a new adventure is now beginning.

Next: Doctor Who: Our First Impressions of the 13th Doctor

Doctor Who season eleven will air on BBC America in fall 2018.