The 1981 treat, which featured cream cheese frosting, was put under the hammer at Nate D. Sanders Auctions in Los Angeles on Thursday (17Dec15).
The piece of cake, baked by then-Naval Armed Forces baker David Avery, was bought by a collector, who was handed the item in a silver monogrammed presentation box with the original gift note, which reads: "With best wishes from Their Royal Highnesses The Prince & Princess Of Wales."
Auctioneer Sam Heller tells Hello! magazine, "Collectors are willing to pay a premium to own a piece of history from the most famous wedding of the 20th century."
Auction house bosses previously sold a slice of Charles and Diana's wedding cake last year (14) for the same price.