PARIS A long-lost painting by 17th-century Flemish master Peter Paul Rubens has been found in a Paris mansion , a French auctioneer said on Sept. 10. "It is a masterpiece," said Jean-Pierre Osenat, who had made the discovery, referring to the sketch of Jesus Christ on the cross painted in 1613. "It was painted by Rubens at the height of his talent," he told AFP, adding that the artwork was in "very good condition." Osenat, the head of the eponymous auction house, said he had found the painting