Everyone, as Andy Warhol put it, will be famous for 15 minutes. But for one artist, fame - and the attentions of Warhol and his entourage - seems to have been so fleeting as to escape him entirely.

Pietro Psaier apparently spent much time collaborating with the pioneer of Pop Art on works in his studio, the Factory, in New York. According to a British auctioneer, he was integral to the success of the studio, but chose to maintain a dignified distance from the limelight.

However, the guardians of the Warhol estate, which authenticates the artist’s work and looks after his archives, have no such recollection.

Claims by John Nicholson Auctioneers of Psaier’s provenance and connections, which accompany a sale of his work, are being contested by the Warhol estate, which questions if the artist ever even existed.

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The blurb attached to the Nicholson sale of Psaier’s paintings and drawings reads that he “can be closely linked to Andy Warhol, where he worked at his studio, The Factory, in New York, often collaborating on pieces with Warhol”. Such a link would boost the artist’s sale value considerably.

But Tim Hunt, a British curator with the Warhol Foundation, said: “I don’t remember ever seeing anything in the literature or anywhere else.”

Vincent Fremont, a former Warhol associate and member of the foundation’s board, was equally dismissive. “I met Andy in 1969 and became a full-time employee from 1971. I’ve never heard of this guy,” he said.

Nor is there any mention of Psaier in the extensive archives of the Warhol Museum. Matt Wrbican, its archivist, said: “We’ve searched through all his papers. I haven’t ever seen his [Psaier’s] name. Zero. Zilch.”

Noting that Warhol saved almost all his correspondence and tape-recorded conversations, he added: “I have been working with him [Warhol] close to 18 years and I’ve never seen this guy’s name. I’m not sure he ever existed.” In recent years, the Warhol Museum has been contacted by several collectors, most of them British, inquiring about Psaier and wanting to buy his work in Britain. Bonhams has offered three Psaier works since 2005, although they did not have a Warhol connection. Yesterday, there was another sale in London, at a small auction house.

Commenting on the artworks themselves, the archivist said: “They incorporate images Warhol used in his work.” Last week, Wikipedia, the online encyclopaedia, responded to his request to remove Psaier’s biography from its site.

But the website of John Nicholson Auctioneers, which has salerooms in London and Haslemere in Surrey, says that the Italian-born artist was working as a waiter in Greenwich Village when he met Warhol and that “they worked and remained friends until the late 1960s”.

It claims: “Psaier produced layouts, silk screens and joint works at Warhol’s studio, though few artistic or financial rewards would come his way.

“Some critics say that without Psaier and fellow artist Rupert Jasen Smith in the background, Warhol could never have maintained production of the Factory commercial output, but with both dignity and style neither men chose to take the limelight from Warhol.”

The Nicholson website says that the artist died in the 2004 tsunami, that his remote beach house on the coast of Sri Lanka was swept away and his body never found. But observers have been noticing increasing numbers of his works coming up for sale since.

In April, Nicholson sold more than 200 works by Psaier and says that his prices have increased “drastically” over the past two years, with a new record achieved by a chalk drawing of Marilyn Monroe in red, “a joint work between Pietro Psaier and Andy Warhol”, which sold for £14,000.

John Nicholson, who is preparing the catalogue for a Psaier auction on September 17, claims that he has photographs of Warhol with Psaier, referred to as “Peter the Italian” in his diaries, disputed by Mr Wrbican. Mr Nicholson said: “We have clients who worked at The Factory. They not only remember him, but remember them doing those pictures. I have proof that he was there - proof from Uri Geller [the paranormalist] who knew him when he was there in The Factory.”

Contacted by The Times yesterday and asked whether he knew Pietro Psaier, Mr Geller said: “I’ve never heard of him.”

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