Diana is a non-canonical character who was created for the adaptation of The Manhood of Edward Robinson, the tenth episode of the Thames Television series The Agatha Christie Hour. Like Poppy, Guy, Jeremy, and Sebastian, Diana is also a friend of [Lady Noreen Elliot]] and part of the "burglary for fun" scheme that Noreen had started. It is Noreen's and Jimmy's turn to conduct a burglary in order to win a bet for the prize money. Diana turns up at the Cafe Paris with Sebastian and others to try to frustrate Lady Noreen's plans to prevent her from winning the bet. See the article on Sebastian for details.
This character does not exist in the original story.
The part of Diana is played by Georgina Coombes.