Martin Lang bought the painting purportedly by Russian-born artist Chagall in 1992 and asked BBC's "Fake or Fortune" series to determine if it was genuine, the BBC reported Saturday.
The painting was sent to the Chagall Committee in Paris, an organization run by the artist's grandchildren to determine the authenticity of paintings like Lang's.
They determined the nude watercolor was a forgery and said it would be destroyed by fire.
"I had no idea that anyone would take such a draconian view," Lang said. "They say they want to counter forgery but I think this will have the opposite effect of deterring honest people like myself from coming forward."
Lang said he asked the committee to mark the painting as a fake and return it to him, but he was still waiting for a reply.