The Power of Three (in-universe)

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The back cover of the Series 7 DVD boxset. (COMIC: The Girl Who Loved Doctor Who)
You may be looking for the real world TV story.

In a parallel universe in which the Doctor's life was a work of fiction, The Power of Three was the fifth episode of the seventh series of the television show Doctor Who. It was released as part of the Doctor Who Series 7 DVD boxset. (COMIC: The Girl Who Loved Doctor Who [+]Loading...["The Girl Who Loved Doctor Who (comic story)"])