Coda

A "coda" is a piece added at the end of the general material in question as a concluding event, remark or section.

Due to the original version of the Fourth Doctor story Shada being incomplete and unaired in 1980, the story had multiple attempts at a remake, latest being in 2017 with animation, with Tom Baker returning to his role in a live coda filmed as an extra to the now-finished story.