Photos were published last Friday in French magazine Closer depicting Kate Middleton sunbathing topless.
St. James's Palace confirmed the pictures were genuine and today released a statement confirming the couple are taking legal action:
"We can confirm that a criminal complaint has been made to the French Prosecution Department today.
"The complaint concerns the taking of photographs of The Duke and Duchess of Cambridge whilst on holiday and the publication of those photographs in breach of their privacy."
On top of these criminal proceedings, it is expected that a civil case will be brought against the magazine for damages.
Although privacy laws in France are very strict, the maximum fine for breach of privacy laws is just €45,000 (£36,000) which can easily be made back in sales of the magazine.
Following Closer, Italian magazine Chi and the Irish Daily Star also printed the photos this weekend.
The Duke and Duchess are currently in Solomon Islands as part of a royal tour.
Read more: Kate Middleton topless photos: Duke and Duchess of Cambridge to sue
Read more: Kate Middleton: French magazine to publish topless photos of Duchess
Check out our gallery of Kate Middleton and Prince William arriving in Singapore to begin their Diamond Jubilee tour below: