A famous engraver etched a tiny picture of Jane Austen on some five pound notes.
Each one is estimated to be worth £50,000 (NZ$86,000), judging by the value of some of his other work.
Across Britain, people checked their fivers to see whether they had one of the four special notes.
The third one has now been found by an elderly Northern Irish woman, and she has kindly donated it to charity.
She sent it back to Graham Short, who engraved the notes, with a note asking him to use it to "help young people".
"£5 note enclosed, I don't need it at my time of life. Please use it to help young people," the kindly woman, who wishes to remain anonymous, wrote.
Mr Short's website reads: "The lady who found the note has surprised us all by sending it to the gallery and asking that it be used to help young people. So Graham and the Gallery will be working closely together to do so.
"Currently contacting outlets connected to Children in Need to try and give this to a good cause so we honour the request of the lucky woman who originally discovered the note.
"Stay tuned for more information as the story develops over the following days!"
The elderly woman didn't want to be famous, but just wanted her fiver to do some good.
"An old lady found it and she said 'I don't want my picture in the papers' and she said 'if it sells for a lot of money it will be better if young children could benefit from it'," Mr Short told the BBC.
Mr Short spent one of each of the four special fivers in England, Ireland, Scotland and Wales.
They have been found in Ireland, Scotland and Wales but the five pound note he spent in England is still yet to be retrieved.
Mr Short's friend and fellow artist, Tony Huggins-Haig, who launched the project, said around 5000 people have called up falsely claiming to have found it.
The series number of the remaining note is AM32885554.
"It would be wondrous if someone finds it who is deserving, who is blown away by it, and who wants to do something worthwhile with it," said 53-year-old Mr Huggins-Haig.
"It's been an incredible and humbling story thanks to Graham, who goes to incredible lengths to create artwork.
"It really is a Willy Wonka story, and one day all four stories will be told, of which the first three are incredible."
All of Mr Short's work is insured for at least £50,000, but Mr Huggins-Haig believes the notes could actually sell for up to £100,000 (NZD$173,000).