“Portrait of a Young Man, around 1513-1514, from the Czartoryski family collection in Krakow, was confiscated by the Nazis in 1939 for Hitler’s Führermuseum, Linz. It disappeared in 1945 shortly before the end of the Second World War.” Polish authorities won’t say where it was found, except that it is “in a region of the world where the law favours us.”