The Final Game (unproduced TV story)

The Final Game was an unproduced serial due to end Season 11. It would reveal that the Doctor and the Master are actually two aspects of the same Time Lord with the Master as either the evil side of the Doctor's personality or his brother, explaining why the Master never sought to actually kill the Doctor and would've ended with the Master sacrificing his life for the Doctor. However, the episode was never produced due to the tragic death of Roger Delgado (the Master) and Planet of the Spiders replaced this story as the final episode for Jon Pertwee (the Doctor).