The photos showed Kate relaxing at a private villa in Provence, in southern France, sometimes without her bikini top and, in one case, her bikini bottom partially pulled down to apply sunscreen.
The royal couple is also filing a criminal complaint against 'X' — the unnamed photographer who took the picture.
The suit aims to flush out the mystery photographer's identity and prevent him or her from spreading the photos to new locations. If the case goes forward, the photographer could face a substantial fine and a one-year prison term.
But fines and prison terms won't remove the photos from the Internet.
Professor Tim Luckhurst, head of the journalism department at the University of Kent, said the royal couple has likely learned some lessons from the debacle.
"The prince and his wife are going to have to think hard about what sort of conduct is acceptable for the heir to the throne and his wife in the age of the Internet," he said.
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