The cake, still in its original white and silver presentation box, was sold online Thursday by Nate D Sanders Auctions of Los Angeles.
With the box was a card stating, "With best wishes from Their Royal Highnesses, the Prince & Princess of Wales." Auction house spokesman Sam Heller says the buyer is a private collector.
Although the cake came wrapped in its original wax paper, Heller says it wouldn't be a good idea to try to eat it.
He adds, however, that there is a small but dedicated group of royal cake collectors.