The Final Game (unproduced TV story)

✅ The Final Game was an unproduced serial intended to end Season 11. It would have revealed that the Doctor and the Master were actually brothers or the latter Time Lord was the former Time Lord's darker personality. This story originally ends with the Master's first major incarnation sacrificing himself to save the Third Doctor's life and then the latter's regeneration. But the episode was never produced due to Roger Delgado's death so TV: Planet of the Spiders replaced this story.

Legacy
Several elements from this episode have been recycled throughout the years:
 * Two elements were recycled in TV: Logopolis:
 * The Master being the Doctor's dark half was alluded when the Fourth Doctor implied this to Adric and Nyssa.
 * The Master causing the Doctor to regenerate occurs when the Master's second major incarnation (protrayed by Anthony Ainley) caused the Fourth Doctor to regenerate.
 * Their possible fraternal relationship was teased in TV: Planet of Fire by the Master's second major incarnation to the Fifth Doctor and Peri Brown but TV: The Sound of Drums dismissed this theory after the Tenth Doctor was asked this question by Martha Jones.
 * The original ending occurs in TV: The End of Time when the Master's sixth major incarnation (played by John Simm) sacrifices himself to save the Tenth Doctor from Rassilon.