It was Kate’s idea, and she used the names to book them into a private holiday home as a birthday treat for Prince William, who just turned 27, reported the tabloid The Sun.

However, the private party turned a bit crowded, when Wills' brother Harry, 24, decided to tag along with a bunch of pals. The romantic dinner plans were shelved, and instead there was booze flowing on the beach.

William and Harry knocked back beer and cider and played football before setting up a fire. William and Kate then watched the sun set, reports the tabloid.

According to a source: "They have been staying at private house under the assumed name Mr and Mrs Smith. "It’s quite funny really that they feel they need to go to such great lengths to keep their visit a secret — but I suppose it adds to the romance." Incidentally, dad Prince Charles and Camilla also famously used to refer to themselves in code as Fred and Gladys.

The group then reportedly headed down to the south Cornish coast to the home near the medieval town of Fowey. The source said: "William and Harry spend a lot of time in Cornwall in summer. They love it. They are mad about surfing and can go to secluded beaches where they can go surfing largely unnoticed.

But this time word quickly spread they were in the area." Kate’s picnic plans also had to take a backseat as the rugby-mad princes decided to find a place to see the Lions take on South Africa. The brothers stunned onlookers at the Royal British Legion club when they turned up to watch the game there. A shocked club member told the tabloid: "Normally you'd have to be a member to get in - but you can't turn royalty away."

Wills, however, spent yesterday afternoon playing tennis with Kate. He and Harry then proceeded to RAF Shawbury in Shropshire, where they are training to be helicopter pilots.