Pictures of Kate Middleton in a bikini showing her baby bump are to be published by an Italian gossip magazine.
St James's Palace has condemned the plans. A spokesman said it was disappointed that the privacy of the Duke and Duchess of Cambridge has been invaded by Chi magazine.
The magazine was at the centre of a storm in in September when it followed the French edition of Closer by publishing images of a topless Kate.
The new batch of pictures show Kate in bikini and baby bump. They also feature her sister Pippa Middleton in a bikini.
Other pictures to be published show the duchess walking along the beach with William. The couple are on holiday on the private Caribbean island of Mustique.
A palace statement said it was a "clear breach of the couple's right to privacy".
"We are disappointed that photographs of the Duke and Duchess on a private holiday look likely to be published overseas," the spokesman said.
Chi was threatened with legal action over the images it published from the royal couple's holiday in France.