Jerry Lewis wrote and directed The Day the Clown Cried but seemingly lost heart in his project
In the early 1970s Hollywood actor Jerry Lewis started working on a Holocaust film so bizarre he ended up hiding all the footage and to this day it has never been seen.
But the BBC has uncovered a large collection of images for an exclusive online documentary about the strange movie, as producer Richard Latto explains.
The Day the Clown Cried told the story of a fictional clown, Helmut Doork, who was thrown into prison and eventually used to entertain children and lead them into the concentration camp gas chambers.
Lewis - at the peak of his career after success in The Nutty Professor and the Bell Boy - wrote and directed the film, and was at first very passionate about the idea. But perhaps even he eventually found the subject matter too harrowing.
The film has never been released, with only a handful of people claiming to have seen anything from the production. Lewis himself avoids questions about it during interviews and public appearances.
For the BBC documentary The Story of Day the Clown Cried, presenter David Schneider went to hear the stories of people close to the production, including the late Lars Amble, who played a Nazi guard.