Doctor Who: Why Each Doctor Was Forced To Regenerate

The most recent regeneration we've seen in the show, the departure of the Twelfth Doctor wasn't just a farewell to star Peter Capaldi: it was a farewell to most of the creative talent that has defined modern Who, such as showrunner Steven Moffat, writer/actor Mark Gatiss, and composer Murray Gold.

This gives Twelve's exit an extra layer of emotion, making an already sad moment feel even sadder. Goodbyes are always hard, but at least Capaldi went out with a bang.

After being laser-blasted by the Cybermen and refusing to regenerate, that aforementioned adventure with the First Doctor helps Twelve come to terms with his impending demise. His companions Bill, Nardole, and Clara appear to see him through to the end, and he returns to the TARDIS, where his regeneration finally begins.

Cue another cracker of a speech from the pen of Moffat and the pipes of Capaldi, a bit of foreshadowing about the Chibnall era ("yes, I know they'll get it all wrong without me"), and an epic slo-mo wide shot of the TARDIS exploding, and before long, the Doctor has transformed into a woman for the first time in the show's history.

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It's always sad when a Doctor leaves, but what about when they first arrive? Check out our ranking of every post-regeneration episode here!