The Duke of Cambridge has branded the decision to publish topless photographs of his wife "particularly shocking" given his late mother's battles with the paparazzi.
William expressed his sadness at the incident more than four years ago in a written statement read to a court in Nanterre, west Paris, where six people are on trial in connection with the alleged breach of privacy.
The long-lens images, taken as they holidayed in the south of France, adorned the front and inside pages of France's Closer magazine in September 2012 alongside an article about the loved-up pair entitled "Oh my God!".
William and Kate were on the terrace of a private chateau in Provence owned by Viscount Linley, the Queen's nephew, when they were photographed.
William, who did not attend the trial, has asked for €1.5m (£1.3m) in damages from the magazine as well as a further €42,000 (£35,400) from a local newspaper in Provence which also ran the pictures but with Kate's breasts covered up.
In a written declaration read in French in court by the couple's lawyer Jean Veil, William said: "In September 2012, my wife and I thought that we could go to France for a few days in a secluded villa owned by a member of my family, and thus enjoy our privacy.
"We know France and the French and we know that they are, in principle, respectful of private life, including that of their guests.
"The clandestine way in which these photographs were taken was particularly shocking to us as it breached our privacy."
He added that the images were "all the more painful" given the harassment linked to the death of his mother, Diana, Princess of Wales.
William ended his statement by thanking the French authorities for their support and work on the investigation.
All the defendants are facing criminal charges of invasion of privacy and complicity but deny causing any damage.
The verdict is expected next week.