A woman from Upper Saddle River, New Jersey stands to benefit from the sale of “Wilted Sunflowers,” one of the Austrian painter Egon Schiele’s most important works, which disappeared when her family fled from the Nazi invasion of Austria more than 65 years ago.

Schiele’s “Herbstsonne,” or “Autumn Sun II,” inspired by Vincent van Gogh’s “Sunflowers,” which was one of a half a dozen Schiele pictures thought to have been destroyed in World War II, was sold this week at Christie’s in London for more than $21 million.

It was put on the market by descendants of Karl Grunwald, an Austrian Jewish antiques dealer who escaped his country when the Germans invaded in the 1938 Anschluss. A van loaded with his art collection was looted by the Nazis on its journey through France.

Painted in 1914, the picture was bought by Mr. Grunwald, from Schiele whom he had befriended during World War One and helped by obtaining for him non-combat posts.

“An artist in the army is like a fish out of water,” co-director of the Galerie St. Etienne in New York and author of the first comprehensive Schiele catalogue raisonne, Egon Schiele: The Complete Works, Jane Kallir, said. Mr. Grunwald “essentially allowed him to resume his career as an artist rather than serving as a soldier.”

Schiele went on to paint an oil portrait of Mr. Grunwald, and watercolor portraits of his family.

According to Christie’s, the painting was confiscated by the Germans in Strasbourg and was auctioned in 1942. The picture, considered to be one of Schiele’s masterpieces, then disappeared.

Mr. Grunwald, who eventually found his way to America, spent much of his life trying to recover his art collection. Though he was only partially successful – he managed to recover the portrait Mr. Schiele painted of him – he could not find the “Herbstsonne” before his death in 1964, when the quest for his art was continued by his family.

Ms. Kallir, whose grandfather fled Austria and started the Galerie St. Etienne, from where Schiele first began to gain popularity in America, told the Grunwald family that she would help recover the painting, but “I really considered it a lost cause,” she said.

The painting surfaced unexpectedly when a Frenchman, who wishes to remain anonymous, contacted Christie’s to have the painting valued with the intention of putting it up for auction. Christie’s experts, who at first assumed the picture was a copy, told the owner they were surprised to discover it was the original. “It was an intense experience, a rare moment of magic,” Christie’s expert Thomas Seydoux said.

“That this should turn up as it did, almost without any fanfare or ceremony is totally miraculous,” Ms. Kallir said.

Christie’s put the French owner in touch with the Grunwald family and the picture was returned to them. Karl Grunwald’s heirs sold it through Christie’s on Tuesday. The sale to a private buyer came in well over the estimated price of between 5.4 and 11.1 million dollars.

“It was fantastic. We were absolutely delighted. We were thrilled with the price,” Christie’s Christina Freyberg said.

As well as in Upper Saddle River, New Jersey, relatives of Mr. Grunwald live throughout America, including in Scottsdale, Ariz., as well as in France. They could not be reached for comment.