A trial must be held to determine who is the rightful owner of a painting by a Dutch master that was stolen by the Nazis from a Polish prince’s family collection, a New York judge has ruled. The prince will have to show that his family made diligent efforts to locate the painting after the war, the judge said.

Donald Turcotte, a Cornell University professor, received the painting, “Portrait of a Lady, Presumably Anne of Bretagne” by Jan Mostaert, from his mother, who bought it in 1959 from the M. Knoedler & Co. gallery in New York. When Mr. Turcotte consigned it for sale at Sotheby’s, the auction house, in their January 1997 Old Masters sale, Prince Adam Karol Czartoryski-Borbon saw it in the catalog and claimed the painting was one that had been stolen from his family by the Nazis during the German occupation of Poland.