Camilla Parker-Bowles, Prince Charles' long-time mistress, had been invited to join the party but not the publicity, reports CBS News Correspondent Richard Roth. It has turned the 10-day holiday into a royal family affair.
"It is very significant because it's the first holiday that the Prince of Wales has ever taken Camilla away with his children," says Jane Kerr, the royal correspondent for Britain's Mirror newspaper.
The queen was reportedly not amused. Some reports say Prince Charles did not even warn his mother, knowing she is worried that Camilla's role in his life has implications for the British crown.
What haunts Buckingham Palace is the memory of another Mediterranean cruise almost 70 years ago, another Prince of Wales, and another divorced woman.
Prince Edward's public holiday with his American lover Wallis Simpson is a reminder of how royal romance can become a scandal big enough to rock the throne; Edward eventually gave up the crown for Simpson's love.
The rules are different now, of course; the public is not so easily shocked. Additionally, this summer's vacation will be absolutely private, according to palace officials.