The 28-ounce slice, preserved in plastic wrap and stored in a decorative tin for 40 years, is going up for sale August 11 -- and the winning bid is expected to come in at a cool $700.

The slice of wedding cake going up for sale was given from the Queen Mother (Queen Elizabeth's mom) to Moyra Smith, whose family sold the cake in 2008 to a collector.

the piece comes with a royal wedding breakfast program, details on the ceremony and an order of service for the wedding.