Dr French is a non-canonical character who was created for the the BBC 1985 adaptation of the novel which formed part of the Miss Marple series. Dr French was the doctor who examined the body of Rex Fortescue after his death. He quickly came to the conclusion that he Rex had been poisoned by Taxine.
The part of Dr French is played by Louis Mahoney. In the original story this role is undertaken by Professor Bernsdorff.