It turned out to be a Victorian sovereign worth £200.
Robert, 12, said: "I knew it wasn't a pound and I thought it was a foreign coin. I took it home and showed it to my dad. He thought it was a sovereign and we decided to take it to Lyon & Turnbull auctioneers. When they said it was worth probably £200 I couldn't believe it."
The coin will be auctioned on March 13 in Edinburgh.
Colin Fraser, of Lyon & Turnbull said: "This is a fine example of a Victorian gold sovereign. It is the first time I have heard of anyone finding one in their change."
Picture: Jamie Simpson.