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Given the following post, respond as if you're commenting on Reddit:
human
[Doctor Who] What number regeneration is the Doctor on?

In doctor who I've heard the doctor has started his regeneration cycle over again because River Song gave him all her regeneration and I've also heard he is number 13 instead of 1. Can somebody explain this to me better?
gpt
He's on 13.

And it wasn't River who did it. She sacrificed her regeneration to keep #11 alive. #13 was something given to him when he saved Gallifrey from destruction - *how* it was down is unknown.

EDIT: Changed #12 to #11, since the War Doctor is unnumbered. Damn timey wimey crap.