The BBC's Nicholas Witchell reports that it's thought the Queen was not told about the holiday

The couple are rarely seen together in public, but there has been intense speculation about their relationship since the death of Diana, Princess of Wales.

Camilla and her children, Tom and Laura, are reported to be with Charles and his sons, Prince William and Prince Harry, aboard a 400ft mini-liner in the Greek islands.

It marks another step by Prince Charles to formalising his long-term relationship with Camilla Parker Bowles.

Three British newspapers carry extensive reports on the story.

The story is extensively reported in British newspapers

One quotes a friend of Camilla as saying: "She sees the break as another significant step in winning acceptance for her relationship with Charles."

Charles and Camilla's relationship is gradually becoming more public.

The Prince of Wales admitted his adultery with her during a television interview in 1994.

Camilla and Andrew Parker Bowles divorced the following year and Mrs Parker Bowles became a regular visitor to the Prince's Highgrove home.

But it was not until earlier this year they stepped out together in front of the cameras for the first time after attending a party at the Ritz hotel in London.

The carefully-planned scene was seen as a sign of Charles's determination that Camilla should be accepted as his partner in the wake of Diana's death.

According to the reports, 17-year-old Prince William had suggested that Camilla join the holiday cruise.

Camilla is reported to be growing closer to both William and Harry, with royal watchers saying that she and Charles are slowly "normalising" their relationship.

Last week, Charles and his sons held a photocall outside their Highgrove residence, in the hope that journalists and photographers would then leave them in peace for the summer.