A slice of wedding cake from 1981 that was one of 23 cakes served at Princess Diana and Prince Charles' Royal Wedding has been auctioned off. Are you ready for this? It SOLD for over $2,500. The owner will keep it preserved as a keepsake and likely not take a bite like Elaine did on Seinfeld! Prince Charles and Lady Diana Spencer married on July 29, 1981 at St. Paul's Cathedral.