Banksy, the graffiti artist, gave a £200,000 painting to a band after he accidentally "stole" their name as the title to his new film, Exit Through the Gift Shop.
It turned out that the mystery man was the elusive graffiti artist and the band agreed to change their name.
They have now rebranded themselves as Brace Yourself.
Keeping his promise, Banksy then sent a huge painting to his home featuring a black and white Grim Reaper driving a dodgem car.
The Banksy painting has been valued at £200,000 but the band plan to display it at a gallery rather than sell it.
''We had these hilarious emails from someone saying he was Banksy but we didn't know if they were genuine," said Mr Duncan, 41, from London.
''Then a scruffy white van arrived. The driver had no idea what he was carrying. When we saw the painting we could not believe it.
''We had to insure it, so a man from Sotheby's came over to see it in my loft."
He added: "He said to me, 'this is surreal. I have just been valuing an 18th-century portrait in a stately home, but it is not as valuable as this'.''
Banksy's works routinely change hands for hundreds of thousands of pounds and fans of his stencils and installations include Brad Pitt and Angelina Jolie.
On Tuesday council cleaners in Melbourne were left embarrassed after they accidentally painted over an original Banksy artwork from a city building by mistake.