Is art collector Dmitry Rybolovlev an unwitting victim of fraud, or a savvy buyer who should have known what he was getting into? Was Yves Bouvier acting as his buyer’s agent, or simply as a dealer?

Depends on whom you ask. Which roles the men were playing as Rybolovlev bought hundreds of millions worth of paintings in recent years from Bouvier is at the heart of a feud that has gripped the art world, with previously unreported legal documents adding fresh ammunition to the battle.

Rybolovlev, a Russian fertilizer billionaire, accuses Bouvier, an art-world heavyweight who runs duty-free storage facilities from Geneva to Singapore, of overcharging him by $500 million to $1 billion during the course of a decade for works by Mark Rothko, Leonardo da Vinci and Pablo Picasso.

Rybolovlev has said in Monaco legal filings that he considered Bouvier his agent and that Bouvier betrayed that trust by repeatedly charging hidden markups of tens of millions of dollars. Bouvier and his lawyers have countered in interviews and court documents that the two never had a written agreement and engaged in hard-nosed business discussions between a seller and a good repeat buyer willing to pay market prices for top works.

Monaco Documents

Bouvier’s characterization of Rybolovlev as a sophisticated investor is supported by documents that Monaco prosecutors are reviewing in an investigation they launched after the collector filed a criminal complaint alleging fraud by Bouvier.

The Russian billionaire was authorized to appraise art, negotiate sales and participate in auctions on behalf of two of his family trusts because of his “expertise” and “special knowledge” of paintings, drawings and antiques, according to power-of-attorney documents signed by those trusts in 2005 and 2010.

The British Virgin Islands-based trusts empowered Rybolovlev to use his “special knowledge in any kind of artwork including but not limited to paintings, drawings, statues and antique furniture, investments in art and valuable items” to act on their behalf, including in negotiations with dealers and representatives of private art collections.

Rybolovlev’s art knowledge is beside the point, according to his camp.

“The level of art expertise of any of the victims of this massive fraud is irrelevant,” said a spokesman for Rybolovlev. “The underlying dishonesty resides in the structure of the hidden margins amounting to $1 billion, and how the victims were made to believe that these secret margins were part of the purchase price.”

A spokeswoman for the Monaco prosecutor’s office confirmed the investigation is ongoing and declined to comment further.