For more than 60 years, the Grunwald family hunted for Wilted Sunflowers, a masterpiece by Egon Schiele, seized from them by the Nazis and lost in the turmoil of the war.
Even on his death bed two years ago, Frederic Grunwald - son of Karl, who had bought it before the Second World War - asked his family not to forget the painting. And yesterday, two generations of the family stood in awe before the work after it re-emerged, by chance, when a private owner contacted Christie's auctioneers for an evaluation, having no idea of its history.
While other restitution cases have spent years in the courts, the anonymous owner immediately - and unusually - handed it over to be returned. The work becomes only the third from Karl Grunwald's once sizeable collection to be traced.
It will now be the highlight of the Impressionist and Modern Art sale at Christie's, London, on 20 June, where it is conservatively expected to make at least £6m. A Schiele watercolour sold earlier this year for £4.1m.
Cory Pollack, Karl's granddaughter and Frederic's daughter, who had flown with her family from America to announce the rediscovery yesterday, said they were "absolutely thrilled".
"This is something that has become our family legacy. We've talked about it for years," she said. "My father had talked about it literally as he was dying. 'Please, don't forget the Sunflowers, please try to find them,' he said. Our biggest fear was that it was destroyed or lost. But we always hoped that it would show up one day."
Sonnenblumen, or Wilted Sunflowers, was painted in 1914 and was subsequently acquired by Karl Grunwald, an Austrian collector based in Vienna. He and Schiele became firm friends and the artist used Karl Grunwald as a model, including for a painting which the dealer himself acquired.
When Hitler annexed Austria in 1938, Mr Grunwald fled Vienna for France and arranged to move his art collection of at least 50 paintings to safety.
But unfortunately the collection, including the current work, was confiscated in Strasbourg, where the Grunwalds had kept it in storage, and sold.
Karl Grunwald survived the war, although his wife, Steffany, and their daughter, Leny, died in a concentration camp, and searched assiduously for his looted art. Frederic, one of his four children, took over the hunt upon his death in 1964.
Schiele's portrait of Grunwald subsequently emerged at auction and a settlement was made. The family also reclaimed a painting by Gustav Klimt after a 13-year battle with a museum in Strasbourg.
Yet the whereabouts of Wilted Sunflowers remained unknown. "It had become increasingly unlikely to imagine that it would publicly resurface," Jussi Pylkkanen, the president of Christie's Europe, said yesterday. Then at the end of 2005, the owner, who had no particular knowledge of the arts, contacted Christie's for a valuation. Looking at the supplied photograph, experts initially thought that it was a copy.
But when Andreas Rumbler and Thomas Seydoux went to see it in modest surroundings in a small apartment in France, they discovered it was the original, missing Schiele.
"We entered the apartment, took one look at the picture and immediately turned to each other, incredulous," said Mr Seydoux. "There was no doubt we were standing in front of the Schiele masterpiece. It was an intense experience, a rare moment of magic."
Mrs Pollack, who will share the proceeds with other members of the family in the United States and France, said it was a wonderful thing to get it back. "It's part of the healing process," she said. "The picture for us is not about money."
Seeing the work had been incredibly emotional, she said. "It would be wonderful to keep it, but, truthfully, what is more appropriate is for it to be in a venue where many other people can appreciate it as well," she said. "That would be our wish."
The artworks looted by Hitler's henchmen
Hermann Goering, founder of the Gestapo, led the Nazi plunder of art. Coming from a wealthy family and with a love of art, he took the opportunity created by the war to acquire thousands of objects confiscated from museums, art dealers and private collections.
Particular favourites were female nudes and Gothic art, but his collections also included Roman artefacts, 19th-century German paintings, jewellery and tapestries. He appointed agents throughout Europe to scout for him and accumulated around 2,000 works of art between 1939 and 1945. These included pieces such as Lucas Cranach's Venus and Cupid and Rembrandt's Two Philosophers. Works regarded as "degenerate", such as those by Modernists, were exchanged for more acceptable pieces or sold on.
When the war was over, the European art market boomed on the back of these operations.
One example of the claims that followed was the case of Austria v Altmann. Last month, the Austrian government restored five works by Gustav Klimt to Maria Altmann in California, the heir of an Austrian family forced to flee the Nazis in 1930s. She had pursued an eight-year battle to the US Supreme Court. The works, now worth £170m, included a painting of her aunt, Adele Bloch Bauer. The family's heirlooms were seized by the Nazis and had hung at the Belvedere Museum in Vienna. On return, Mrs Altmann immediately lent the paintings to the Los Angeles County Museum of Art, but intends to sell them. The Austrian government had hoped to save the works for the nation but has decided it cannot afford them.Reuse content