Bavarian officials are remaining tight-lipped about an incredible tale of lost modern art worth millions of euros.

The vast trove, containing works by Picasso, Matisse and Chagall, was discovered by chance, rotting among stacks of groceries in a Munich flat.

It had been seized by war-time German art dealer, Hildebrand Gurlitt, whose reclusive son Cornelius sold pieces whenever he was strapped for cash.

Art expert Wilhelm Warning said the pictures are priceless: “They were considered ‘degenerate’ by Hitler’s Third Reich, and their value is incalculable, if they’re not fakes.”

German customs officials made the sensational find in 2011 after a 76-year-old man was found carrying a large, albeit legal, amount of cash.

Ruediger Mahlo, a spokesman for the Conference on Jewish material claims against Germany, in Germany said: “This case shows the extent of organised art robbery in museums and private collections, which were almost all in Jewish possession.”

Experts are now trying to determine the ownership of the art works.

But Bavarian officials have declined to comment on why it took them so long to reveal what could be one of the largest recoveries of Nazi-looted art.