Two bidders battled it out over the telephone for the slice of white toast which is believed to have been served to Prince Charles on the morning of his wedding to Diana Spencer.
The winning bidder paid $350 for the 30-year-old toasted bread.
A spokeswoman for the auction house said: "The slice of toast went to a UK buyer.
"There was a round of applause when the gavel dropped, then it was like 'Oh crumbs ... it's sold!"'
The slice of toast was sold on behalf of Rosemarie Smith, from Derby.
She took it from a tray after visiting her daughter at Buckingham Palace just hours before the royal wedding.
The 83-year-old said: "At the time my daughter was a maid at the Palace and one of her duties was to collect Prince Charles's breakfast tray from outside his room.
"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?"'
"I just wandered into the auctioneers out of curiosity and asked them if it was worth anything," Smith said.
"I was pleasantly surprised to hear them agree with me that it could be of quite some value to royal collectors."
Look at the toast very carefully, take a good look.
We are certain there is a face on that toast.
We see thin lips, a nose and eyes that are closed...
We're not saying it's the Virgin Mary or Jesus, but we see a face, or at least we think we do.
