Hazel Court played the Anton Diffring sculpting scene topless. Only her bare back is shown in the British and U.S. versions, but her breasts are visible in the scene shot for European versions. It was one of the first nude scenes of its kind to be shot in England. They cleared the set and had just a skeleton crew. She said she agreed to do it because the scene warranted the nudity and it was shot beautifully. If had been gratuitous, she'd have refused.
Anton Diffring was the second choice for the role of Georges Bonnet, after Peter Cushing turned it down shortly before filming began. When Cushing claimed illness after breaking his oral commitment, the studio threatened legal action against its biggest star but didn't follow through.
Georges Bonnet was born in 1786.
The film takes place in Paris in 1890.
Largely unsuccessful upon general release, the film has garnered a cult following among "Hammer" fans.