The astonishing discovery of a horde of works of art that had been forcibly taken and sold by the Nazis before and during World War II, happened while I was researching for The Carlswick Affair in 2013. The discovery at the home of Cornelius Gurlitt, the son of a Nazi art dealer and collector, once again highlighted how many items still remain unaccounted for today.  Around 1,500 works, including pieces by Claude Monet, Paul Cézanne and Otto Dix were discovered by tax inspectors in Gurlitt's two houses.

Now, two exhibitions of these works are opening