Italian publication Chi is expected to print photos of Kate Middleton wearing a bikini while on holiday with Prince William on the Caribbean island Mustique.
Chi previously sparked outrage after publishing topless photos of the Duchess while at a private villa in France, despite warnings from the Palace.
The new photos show a visibly pregnant Duchess of Cambridge wearing a bikini. Prince William and the Duchess's sister Pippa Middleton are also among the photos due to be published.
The palace said in a statement: "We are disappointed that photographs of the Duke and Duchess on a private holiday look likely to be published overseas. This is a clear breach of the couple's right to privacy."
The French Closer magazine was the first to publish the controversial topless photos last September, which were then re-used by several publications around the world, including Chi.
Prince William later called for the photographer responsible to be jailed, which may be possible under France's strict privacy laws.
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