After Damien Hirst sold a load of works for $125 million this week, it’s tempting to say the entire art world is one gigantic joke.

But even by these fine standards, the latest story seemed more like the elaborate plot for a novel: that a supposed acolyte of the great Pop artist Andy Warhol — whose works have been auctioned at Christie’s and Sotheby’s — might not have ever existed.

John Nicholson, a Surrey auctioneer, has been forced to postpone his latest sale of works by Pietro Psaier, whom he describes as an “important” and “outstanding” artist of “international standing.”

The Andy Warhol Foundation has said it has never heard of Psaier and entire Web sites are dedicated to proving he did not exist; certainly many of the claims made for him are hard to substantiate. A photograph on Mr. Nicholson’s Web site of Psaier apparently with Warhol only raises further questions: Are these two figures actually sitting together or is it a composite image? After much debate, Wikipedia has even removed Psaier’s entry: Has his 15 minutes of fame run out?

All that does not prove Psaier didn’t exist, of course. Who did what to whom at Warhol’s celebrated Factory might conceivably be lost in a licentious haze; many participants are dead, either from drugs or AIDS. But Warhol recorded his conversations, and there were endless documentaries, and huge amounts have been written about his various hangers-on. Collaborations — such as Warhol’s with the British pop artist Richard Hamilton — are normally very well known.

Until the 1990s there seems to be very little mention of this supposedly important but deeply private artist who, if descriptions are to be believed, led a nomadic and hippyish life, after being born in Italy in 1936.

Yet Mr. Nicholson is adamant. His Web site insists: “Some critics say that without Psaier … Warhol could never have produced and maintained production of the Factory commercial output, but with both dignity and style [Psaier] chose not to take the limelight from Warhol.”

Mr. Nicholson has hired a researcher to corroborate his story and says Psaier died in the 2004 tsunami in Asia, where he was said to be living. He says he has a statement from Psaier’s doctor in Spain contending he met Warhol with Psaier at a gallery in Madrid in 1983.

Whatever the truth, Psaier has proved good business for Mr. Nicholson. In April alone, he sold 200 of his works, including a red chalk drawing of Marilyn Monroe, described as a collaboration between Psaier and Warhol, which went for $25,000. Over the past two years, large numbers of Psaier’s works have come onto the market, apparently through his son, though Mr. Nicholson says he has not actually met him. He adds that these works coming up for auction are among the last from the artist’s estate.

Certainly, bigger art-world figures than Mr. Nicholson are sitting uncomfortably: In 1996 Christie’s sold “Flesh and Frankenstein,” attributed to Warhol and Psaier.

Charles Thomson, a leading member of the Stuckist movement dedicated to sending up and exposing Modern art, has been tracking Psaier for some time and is convinced this is “one of the greatest hoaxes in the history of art. He is the most famous artist who apparently knew everybody whom nobody has ever heard of,” Mr. Thomson says caustically. “For instance, I discovered a now-deleted Web site of Psaier claiming that in 2004 he was living in a retreat in Tibet. This is a few months after he was supposedly swept away in his beach hut in Sri Lanka.”

Mr. Thomson grew intrigued when a friend invited him to an exhibition in Notting Hill of a supposedly “undiscovered” Warhol collaborator earlier this year. Sienna Miller was invited, as she’d played Warhol muse Edie Sedgwick in the film “Factory Girl.” “Everybody was enthusing about Psaier’s work, saying how terrible it is he was never recognized.

“But it reminds me of a stunt pulled off by David Bowie, who produced a catalog of this supposedly forgotten abstract painter, and loads of supposed experts went around saying, ‘I always rated him, you know,’ before it was revealed he never existed.”

However, Mr. Thomson makes clear that he does not believe that Nicholson or any of the other auction houses have deceived us deliberately. Rather, he contends that they, too, are victims of a very clever hoaxer.

In the 1960s, Psaier supposedly came to New York, where he met Warhol and became his lover. Warhol is said to have referred to him as “Italian Pete,” although stalwarts of the Andy Warhol Foundation deny this.

Mr. Nicholson claims that in 1974 Psaier became the second-youngest artist to be awarded the Italian-American Institute of Art 56th annual award in New York, but Warhol experts can find no trace of the institute.

Mr. Nicholson has also said that Uri Geller knew Psaier but, when contacted, Geller denied it.

Psaier has roused controversy before. An electric chair supposedly owned by Warhol and Psaier and bought by the Science Museum was shown to be a hoax.

Mr. Nicholson was standing by his story, insisting he met Mr. Geller while filming “Antiques Roadshow” and that Mr. Geller told him he knew Psaier. “There is a major Psaier exhibition touring the world that has nothing to do with me,” he says. “I’ve had loads of people contacting me saying ‘Who is putting this around, and why?’ Of course he existed.

“Unscrupulous people are trying to blacken his name,” he says. “I can understand why people might say he was not connected to Warhol, and it has been hard to get some of the evidence together. But the doctor’s evidence now confirms that clearly they did know each other and that Psaier lived with one of Warhol’s ex-lovers.”

Many collectors now have an interest in Psaier’s existence, of course. Indeed, one little irony in all of this is that interest in Psaier has shot up, which is all good publicity for the rescheduled auction. Claims that he doesn’t exist are likely to make him far more famous than he ever was in life. Well, for at least 15 minutes.