The note is one of four to feature a tiny engraved portrait of Jane Austen on it which are worth between £20,000 and £50,000.
The artwork’s creator, specialist micro-engraver Graham Short, revealed he spent one of the notes on sausage and egg sandwich in a cafe in Blackwood, Caerphilly county.
But now, the BBC has reported, Short’s office has heard from a lady who found the note.
The woman, who wished to remain anonymous, said she plans to give it to her granddaughter as an investment for when she is older.
The note was spent at Blackwood’s Square Cafe, although it is not known where it was discovered.
This particular note was, rather aptly engraved with a quote from Mansfield Park which read: “A large income is the best recipe for happiness I ever heard of.”
The artist decided to commemorate Austen on the notes as next year marks the 200th anniversary of her death.
The unique engravings can only be seen in certain lights with the author’s picture positioned on the transparent part of the plastic note next to the images of Winston Churchill and Big Ben.
The notes also have quotes from the writer’s work. A microscope is needed to see the images clearly.
The four notes have the serial numbers AM32 885551, AM32 885552, AM32 885553 and AM32 885554.
The others have been spent in a cafe in Scotland, a pub in Northern Ireland and a pork pie shop in Leicestershire.
Anyone in possession of one of the special notes has been advised to contact the Tony Huggins-Haig Gallery in Kelso, which launched the project.
Huggins-Haig told the BBC: “All of Graham’s work has an insurance valuation of about £50,000 at the moment. It’s a reasonable estimate.
He added: “It is very much the Willy Wonka golden ticket.”
Short’s last work, an engraving of the Queen on a pinhead, sold for £100,000.