Prince William, 24, who is second in line to the throne behind his father, Prince Charles, was traveling with friends from Dover, England, to Calais, France, on the ferry two weeks ago when they were refused access to a club class lounge on the boat because they had not bought tickets for it, and it was full.
The stewardess who denied them entry failed to recognize the prince, one of the best-known public figures in Britain, even though staff on the ship had gossiped that a member of the royal family was on board.
"If he was getting mobbed on board and people were making life a misery, we would have said, `Come into the club lounge and get away from it'," a P&O spokesman said.
But, he added, the stewardess was not in trouble for failing to recognize the prince.
"We think it's hilarious," he said, reports AP.
"He wasn't hammering on the door and wasn't asking for special treatment," the spokesman said on condition of anonymity. "They had made their own arrangements. Clearly they decided to be discreet."
A spokeswoman for Prince Charles' Clarence House office confirmed that William had been aboard the P&O ferry but refused to comment about what had happened there.