Hitler's Venus

Thanks to research by Dr Birgit Schwartz, the National Gallery in London has learned that one of its paintings - Lucas Cranach the Elder's Cupid complaining to Venus (c.1525) - was once in Adolf Hitler's private art collection. The gallery bought the painting from New York dealers E & A Silbermann in 1963. It seems that in 1945 American war correspondent Patricia Lochridge Hartwell was allowed to take it from a warehouse full of art which was controlled by US forces in Germany! Thanks, guys. This explains its trip to the USA. But where did Hitler get it from? The National Gallery wants to know if anyone can resolve this mystery.