The cake is thought to be the only surviving item from the 1871 wedding of Queen Victoria's fourth daughter, Princess Louise, to the Marquis of Lorne.
It went on sale for 145 pounds ($215) Thursday at the Antiques for Everyone fair in Birmingham. The seller is antiques dealer John Shepherd, who bought it from a private seller.
"I like unusual objects with history," said Shepherd. "This was obviously treasured by the Royal Family, and I believe things should be treasured and looked after."
The slice, which is one-inch thick and protected by parchment, is a tiny portion of the towering 5-foot cake served at Princess Louise's wedding. The entire cake originally weighed over 225 pounds (102 kilograms) and took three months to create.
The wedding caused an uproar when Princess Louise angered the Prince of Wales by becoming the first British princess to marry a commoner. She was determined not to be burdened by the ritual of marrying another royal.
The purchaser will be able to do whatever he wants with the slice - but event organizers suggest it would not be wise to gobble it up.
"We advise them not to eat a 138-year-old piece of cake," said Amy Kiernan, a spokeswoman for the fair.
Get Action News on your website
