St James's Palace has said it is "disappointed" that new pictures of the Duke and Duchess of Cambridge on holiday are to be printed abroad.
Italian magazine Chi plans to publish photographs of Kate, who is expecting a baby in July, in a bikini.
A spokesman for the palace said the pictures were taken "from a distance" as she enjoyed a private holiday with her husband, Prince William, on the Caribbean island of Mustique.
"This is a clear breach of the couple's right to privacy," the spokesman said.
Last year, Chi, which is read by 3.6m people every week, published a series of photographs of the Duchess sunbathing topless on holiday in France.
The magazine, which followed the French version of Closer in publishing the pictures, defended the move, describing Kate as a "Greek goddess".
Its editor, Alfonso Signorini, said at the time: "I really don't see what all the fuss is about."
The Duke and Duchess were later granted an injunction by a French court, preventing Closer from printing more photographs of the couple at the private villa in Provence, France.
The magazine was ordered to hand over all copies of the pictures within 24 hours and banned from selling them on to publications in countries where they had not already been published.
Sky News Correspondent Jason Farrell said: "While Chi speculates these latest pictures are the first to show Kate's bump, partially shaded by her husband, the Duchess looks her usual slim figure.
"It once again opens the debate over the couple's right to any kind of private life.
"There was near universal condemnation when France's Closer magazine first published the topless photos last September.
"In these latest photos, the Duchess is slightly more covered up and that makes a difference. Even the palace statement is less angry."
The tiny island of Mustique has 100 luxury villas, some of which cost \$40,000 (£25,500) a week to hire.
It is described as a "sanctuary" where visitors can enjoy a "relaxed yet elegant lifestyle free from the stresses of the outside world".