Bikini row ... Prince William and Catherine, Duchess of Cambridge.

Bikini row ... Prince William and Catherine, Duchess of Cambridge. Photo: Reuters

Britain's royal family on Tuesday expressed disappointment after an Italian magazine said it would print paparazzi pictures of Prince William's wife Catherine showing her pregnant belly.

St James's Palace said the move by Chi magazine, which is owned by former Italian prime minister Silvio Berlusconi, breached the royal 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," a St James's Palace spokeswoman said in a statement.

Magazine row ... the front cover of Chi with the picture of the Duchess of Cambridge blacked out.

Magazine row ... the front cover of Chi with the picture of the Duchess of Cambridge blacked out.

"This is a clear breach of the couple's right to privacy."

A preview of the cover of Chi magazine, shown on the website of its publisher Mondadori, shows Kate and William in swimwear on a beach on the holiday island of Mustique.

Over a picture of the former Kate Middleton in a blue bikini walking through shallow waters, the headline says: "The belly grows."

It is understood that the magazine has also run pictures of Kate's sister Pippa who is on holiday with the Royal couple and the rest of the Middleton family including her parents Carole and Michael.

Chi is infamous for running salacious paparazzi shots that few other publications will touch, including a number of Royal 'exclusives' that have caused international outrage.

The couple are expecting their first child in July. Kate, 31, was admitted to hospital in December with severe morning sickness but is now said to be recovering.

Britain's royal family launched legal action last year against French magazine Closer over topless paparazzi pictures of Catherine sunbathing in bikini bottoms on the balcony of a chateau in France.

AFP