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* ContentLeak: The episode was leaked early after a BBC America store accidentally sent out the season 7 box set two weeks before the episode aired. Despite Creator/StevenMoffat asking for people to not reveal anything, one newspaper revealed spoilers from the episode including the reveal of Creator/JohnHurt as a new Doctor.
* EnforcedMethodActing: Creator/AlexKingston actually slapped Creator/NeveMcIntosh for real when River slaps Madame Vastra to wake her up. The stage direction for the moment ended with a cheeky "Good luck, Neve!".
* WhatCouldHaveBeen:
** Creator/MattSmith's contract had actually ended with this series, meaning he had to go through the usual guest star negotiations despite him having two episodes left to film. As a backup plan in case he and the previous Doctors who were the primary guest stars weren't able to come to terms, [[https://io9.gizmodo.com/steven-moffat-on-his-desperate-backup-plan-for-doctor-w-1822161779 an alternate ending was written]]: The Doctor completely vanishes from the space-time continuum after rescuing Clara, leading into a MilestoneCelebration that hinged upon Clara remembering the Doctor back into existence via encountering "various fictional forms" of him played by other actors via StuntCasting. Yes, Creator/JennaColeman almost had to basically carry the entire 50th Anniversary Special by herself.
** Originally, Creator/StevenMoffat confirmed that the rift in the Doctor’s tomb on Trenzalore could travel back to the last day of the Time War. Once Clara had been splintered and scattered throughout the Doctor's life, he didn't enter the rift to save her. Instead, Clara returned, but screaming about knowing who the Doctor really is. This made the Doctor decide to return back to the Time War through the rift, leading into the anniversary special.
** The episode was supposed to end with a scene of Eleven carrying Clara out of his timestream and back into reality. The scene had to be cut before filming due to Creator/MattSmith injuring his knee.

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