Gallifrey's moon

According to the work of one Gallifreyan author, the First Doctor took Gallifrey's moon with him when he escaped Gallifrey, along with the President's daughter, the Hand of Omega, the validium, and the faulty Type 40 TT capsule which he used to make his escape. (PROSE: A Brief History of Time Lords)

Across its history, the planet Gallifrey in fact had at least three moons. An unnamed satellite, the heavily industrialised Pazithi Gallifreya (COMIC: Agent Provocateur) and the lost moon, Botoya. Built into the latter was a device that could rewrite history on a grand scale, which was why the Doctor suspected the ancients of Gallifrey had hidden the moon. Botoya subsequently became a legend in Gallifreyan culture, one not widely believed in. (AUDIO: The End of the Beginning)

Missy claimed to Clara Oswald that she had cared for the Doctor "since the night he stole the moon and the President's wife" amongst others. (TV: The Magician's Apprentice) The Twelfth Doctor claimed that it was a lie from the Shobogans that he had stole the moon and the President's wife, clarifying that it was the President's daughter and that he did not steal the moon, he lost it. (TV: Hell Bent)

Human historians who studied the Daleks in the post-Time War universe understood that the Doctor had stole a TARDIS, lost the moon and travelled to Skaro. (PROSE: Dalek: The Astounding Untold History of the Greatest Enemies of the Universe)