The German investigators still combing through the art hoard that Cornelius Gurlitt kept for decades have finished their probe into the history of one piece in the collection of over a thousand artworks. They confirmed that a Henri Matisse painting was stolen by the Nazis.

Matisse’s Femme Assise (Seated Woman) was among the collection Gurlitt kept in his Munich apartment. The BBC reports that investigators have determined that the piece rightfully belongs to a Paris art dealer’s family. Ingeborg Bergreen-Merkel, who is leading the investigation, said that the piece was taken from Paul Rosenberg.

According to the Associated Press, the Rosenberg family’s attorney said that authorities did not tell them about the findings before going public. He does expect it to be returned, but is not sure when that will happen.

Rosenberg’s granddaughter is French TV journalist Anne Sinclair, who is the ex-wife of former IMF chief Dominique Strauss-Kahn.

Gurlitt’s hoard was discovered in 2011, but German authorities waited over a year to go public with the discovery. He died at age 81 in May and was the son of Hildebrand Gurlitt, an art dealer who worked with Adolf Hitler.

Bergeen-Merkel’s team still has around 1,280 paintings left to investigate.