Peter Capaldi's time as the Doctor has come to a spectacular close. The Doctor Who Christmas Special has welcomed Jodie Whittaker as the wandering Time Lord's next incarnation.

Regeneration has always been a lottery, but until this year the Doctor has remained a man. That's now changed, with Whittaker stepping into the Time Lord's shoes as the next Doctor. The Christmas Special, Twice Upon A Time, brought a close to the Capaldi era. Naturally, the episode ends with a spectacular regeneration sequence, and we even hear Whittaker's first words.

Doctor Who is one of the BBC's most successful series. Regeneration stories are key moments in the franchise's history, and Whittaker's casting has led to intense debate among fans. Understanding the level of interest, as soon as the BBC had aired the show they chose to share the key scene on social media.

Doctor Who was relaunched in 2005, reinventing itself for the twenty-first century. The budget was bigger, the effects were more spectacular, and the plots frequently wove their way through entire seasons. Regeneration itself has changed in the relaunched series. Hartnell's first regeneration was a quiet, sedate affair; he simply collapsed, and his companions watched on in awe. In the relaunched series, regenerations are eye-catching events, accompanied by flares of energy. Twice Upon A Time sees possibly the most destructive yet, as the delayed regeneration literally destroys the TARDIS console room.

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Nobody remembers a regeneration because of the special effects, though. The best regeneration stories give the latest incarnation a chance to bow out in style. Since the Tennant era, they've served as an opportunity for the showrunners to tie the last plot threads together. Twice Upon A Time is a classic example, with Capaldi's Doctor saying goodbyes of his own. In a scene that's reminiscent of The Caves of Androzani, Capaldi bids farewell to his lost friends and companions. There's even a touching moment in which his memories of Clara are finally restored.

Capaldi's mercurial Doctor closes with wise words for his next incarnation.

"Run fast. Be kind. Doctor... I let you go."

It's a beautiful touch, with the Doctor looking beyond himself, recognizing his impending "death," and wishing the next Doctor the best. Fans hang on every Doctor's last words, seeing in them a powerful symbol of everything that Doctor stood for. For Capaldi's Doctor, it's impossible not to see this as a fond hope for the franchise's future.

Whittaker's first words as the Doctor are powerfully symbolic. Looking at her face in the mirror, she gives a simple assessment:

"Oh, brilliant."

The idea of a female Doctor has been a frequent topic of discussion ever since Tom Baker decided to leave the role. Seeking to kick up a fuss, he told the press that he wished his successor — "whoever he or she may be" — all the best. He made that statement back in 1981, and the idea has rumbled in the background for over 30 years. Now, finally, we have a female Doctor. And the Doctor's own assessment is simple: it's brilliant.

The Capaldi era has come to a close, and showrunner Stephen Moffat has ended his run as well. It's time for Doctor Who to reinvent itself once again, and the age of Jodie Whittaker has begun.

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