As Revlon magnate Ron Perelman’s case against art dealer Larry Gagosian rages on, Perelman just filed a subpoena of dealings between Colombian mega-collector Jose Mugrabi (who owns 800 paintings by Andy Warhol), his sons David and Alberto, and Gagosian, the New York Post reports.

Gagosian sued Perelman in September 2012 in New York state Supreme Court, claiming that the billionaire went back on a deal to buy two artworks for over $23 million and offering in exchange less money and other art works. In September 2011, Perelman agreed to buy Leaving Paphos Ringed With Waves (2009), a $10.5 million Cy Twombly painting for $250,000 cash, plus four other artworks, as well as a $12.6 million Richard Serra sculpture called Junction (2011) for $4.75 million cash plus five other artworks. Perelman sued Gagosian and his gallery the same day, accusing both of hiding essential information and distorting art prices. Gagosian argued that Perelman was too shrewd a businessman to fall for something like that.

Though the gallery ultimately dropped its case against Perelman and sought to have Perelman’s case thrown out, in February of this year the judge, Barbara Kapnick, allowed Perelman’s case to go forward. The judge found that Perelman and his associates at MAFG were “sophisticated art collectors and investors,” but nonetheless held that it was not unreasonable for Perelman to rely on Gagosian to establish the prices for his artists.

The recently filed subpoena involves the sale of the Twombly painting. Perelman claims that when he first went to buy it for the quoted price of $8 million, he was told that it was already sold, according to the Post, but then a few months later it was back on the market for $11.5 million. Perelman negotiated the price down to $10.5 million but still thought he was getting cheated. Perelman believes the first buyer was Jose Mugrabi and that Mugrabi, along with his two sons, was in cahoots with Gagosian. In an effort to see how the deals between Gagosian and the Mugrabis were handled, Perelman has subpoenaed them asking that they turn over all documents related to their dealings beginning in January 2010.

The Mugrabis have reportedly forestalled turning over any documents by arguing that their dealings have nothing to do with the Twombly painting that’s at the center of the suit.