Just weeks after the scandal about pictures of Britain's Prince Harry naked in Las Vegas, a magazine has sparked fresh controversy by publishing pictures of Prince William's wife, Catherine, topless while vacationing.

The Duchess of Cambridge is "upset" with the magazine -- a French publication called Closer, a royal source told CNN. Palace officials, threatening legal action, have blasted what they call a "grotesque" invasion of privacy.

The grainy pictures appear to have been taken with a long camera lens while the couple was staying at a private chateau in Provence, in southern France.

They were "hugely saddened to learn that a French publication and a photographer have invaded their privacy in such a grotesque and totally unjustifiable manner," a St. James's Palace spokesman said.

These new privacy controversies have dredged up the royal family's often rocky relationship with the press and put a spotlight on how the palace deals with the media after the tragic death of William's mother, Diana, as she fled photographers in Paris 15 years ago.

"The incident is reminiscent of the worst excesses of the press and paparazzi during the life of Diana, Princess of Wales, and all the more upsetting to The Duke and Duchess for being so," the palace spokesman said.

"Their Royal Highnesses had every expectation of privacy in the remote house. It is unthinkable that anyone should take such photographs, let alone publish them."

St. James's Palace officials told CNN they "believe a red line has been crossed." The palace confirmed that the couple is taking legal action against the publishers of Closer.

The pair remain focused on their Asian tour on behalf of Queen Elizabeth II, he added.

William, who is second in line to the throne, and his wife are in Malaysia as they carry out a nine-day Southeast Asian tour of Commonwealth nations, which started in Singapore.

The photographs cannot be accessed on Closer's website, which shows only the magazine's front cover with heavily blurred images. The photos are featured in the magazine's print copy, which is available in France.

The latest furor comes three weeks after the British royal family was caught up in a media furor over images of William's younger brother, Prince Harry, partying naked in his Las Vegas hotel room with a group of girls.

Those photographs were widely circulated online but were published in only one UK tabloid, The Sun, after palace officials asked UK media not to run them. The Press Complaints Commission, the UK press watchdog, received about 3,800 complaints from the public but said it was inappropriate for it to take any action without a formal complaint from the palace.

The Sun has made clear that it won't publish the pictures of Catherine, however. Editor Dominic Mohan tweeted: "The Sun has no intention of breaching the royal couple's privacy. The circumstances are very different to those relating to the photos of Prince Harry in Las Vegas."

Laurence Pieau, editor-in-chief of Closer in France, posted several comments on Twitter late Thursday promoting the release of the topless pictures of Catherine.

One said: "The world exclusive of #closer tomorrow is Kate Middleton as you have never seen her ... and as you will never see her again."

Another read: "For kate middleton to have tan lines she would have to be wearing a swimsuit!"

Interviewed by CNN affiliate BFM-TV on Friday, Pieau defended the decision to publish the photographs, saying, "We were just doing our job."

The magazine was tipped off about the dates of the royal couple's visit to Provence and sent a photographer, she said. The pair were visible on a terrace from the road.

Pieau said that there had been no debate at the magazine over whether to publish the photos and that she believes they are not degrading, as "they are just like any other couple in love."

She described the reaction to the pictures' publication as "disproportionate" and slammed the British press as "complete hypocrites," since photos of Harry naked were published by The Sun.

Pieau said that there are additional photos that are even more revealing but that Closer is not publishing them for now. The magazine will wait to see if any complaint is made against it, she said.

"I think that what these photos really highlight is the issue of the royal couple's security," she added.

A string of negative comments from members of the public has already been posted on the French Closer magazine's Facebook page.

One, written in French, said: "Your behavior is unacceptable, you're as bad as the English tabloids. You have gone too far with the photos of Kate topless and it will cost you a lot I hope. Shameful."