Sotheby's will head to court in London with dealer Mark Weiss and Mark Weiss Ltd. over an alleged fake Old Master painting that was sold in a private sale. Sotheby's later reimbursed the American buyer for the picture and is demanding that Weiss, who supplied the work to Sotheby's client, repay them.

Reports the Financial Times: "The auction house last year ordered pigmentation tests on “Portrait of a Gentleman”, purported to be by the Dutch painter Frans Hals, after it became suspicious about its provenance. It had sold the painting, supplied by Mr Weiss’s gallery, to a US buyer in 2011 for £8.4m ($10m) in a private sale."

In a separate suit, Sotheby's is also suing Lionel de Saint-Donat Pourrières, the supplier of a painting by the circle of Parmigianino, that the auction house contends is a fake. The buyer of the alleged faux "Saint Jerome" was also reimbursed by Sotheby's for $840,000.

A number of Old Master works came into question last fall after being traced to an unknown French dealer named Giulano Ruffini, 71, who insists, ‘I am a collector, not an expert.’ An investigation is underway into about $250 million worth of art.