Middleton used the pseudonym when booking them into a holiday home last Friday as a 27th birthday present for the second-in-line to the British throne -- but they were joined by some friends, including Prince Harry, 'The Sun' reported.

“They have been staying at private house under the assumed name Mr and Mrs Smith. It is 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,” a source was quoted as saying.

The couple and their friends were staying near the medieval town of Fowey in Cornwall.

“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 that they were in the area,” the source added.

The news came a day after another newspaper reported that William has been hunting for a five-million-pound house in the United States.