Someone is about to pay a lot of money for a decades-old cake. This shows how important Princess Diana's and Prince Charles' wedding were back then.The 28-ounce slice has been preserved in plastic wrap for 40 years and kept in a decorative container for $700. It's not a lot of money for celeb memorabilia but it is a good deal for old cake. What is your opinion?As you can see, the slice still bears the royal coat-of-arms decoration. It looks as though no one has managed to steal a bite.This sale announcement is made on the day that would have marked the 40th anniversary of Charles and Diana. The "Wedding of the Century", also known as the royal wedding, was held July 29, 1981 at St. Paul's Cathedral, London. It saw 3,500 people attend in person. An additional 750 million people watched the event around the globe.A slice of the wedding cake that was up for sale was donated by the Queen Mother (Queen Elizabeth’s mom) to MoyraSmith, whose family sold it in 2008 to a collector.