Rosemarie Smith, the mother of a Buckingham Palace maid, claims to have taken the toast while she was visiting her daughter July 29, 1981, according to the BBC.
Smith, 83, said she has had the slice of bread stored at her Derby home ever since, the BBC reported.
"At the time my daughter was a maid at the palace and one of her duties was to collect Prince Charles' breakfast tray from outside his room," Smith said in a news release, the UK's Metro newspaper reported. "I was with her in the corridor and saw that Prince Charles had left some toast on the tray. I had been thinking about a keepsake from the wedding and saw the toast and thought to myself: "Why not?"'
After the intense interest in Prince William's wedding to Kate Middleton last year and in Queen Elizabeth's Jubilee last month, Smith said she thought the slice of toast could be worth something.
The auction took place Thursday. A spokesman for the auction house told the BBC, "The slice of toast went to a U.K. buyer. There were two telephone bidders fighting it out for the slice. It was exciting."