"Two Riders on a Beach", was painted in 1901 and bought by German property developer David Friedmann. He was arrested in November 1938, shortly after the Kristallnacht attacks against Jews in Germany and Austria.

David Toren, Friedmann's great nephew, remembers seeing the painting the day his great uncle signed over his estate to the Nazis at a villa in what has become present-day Poland.

"I was instructed to wait outside the room in which the paperwork was being signed," David Toren was quoted by Sotheby's as saying. "It was in there, in the conservatory, that I sat opposite the beautiful painting of the two horse riders on the beach."

In 1942 the painting was sold by the Nazi regime and eventually bought by Hildebrandt Gurlitt, an art dealer. He had been instructed by Adolf Hitler to take great works from museums and Jewish collectors.

Monuments men

Three years later, the group formed by Allied armies to protect cultural treasures, "the Monuments Men," found the painting. But it was returned to Gurlitt in 1950, as there was no documentation on its rightful owner. The work of the Monuments Men was turned into a 2014 film directed, produced and written by George Clooney.

In 2012 in a home owned by Gurlitt's son Cornelius, more than 1,500 works including some by Picasso, Monet and Chagall were discovered.

"Two Riders on a Beach" was one of the first of the recovered paintings to be released back to the heirs of their rightful owners. Toren said he and other heirs had decided to sell the painting so it could "pass into a new phase of its story."

"I am 90 years old now and blind so, while the return of the paintings after so many years is of huge personal significance, I can no longer appreciate the painting as I did all those years ago," said Toren, who escaped Germany, grew up in Sweden and now lives in New York.

Sotheby's estimated on Friday that the Liebermann painting could sell for up to $850,000 (771,000 euros) when it is auctioned in London on June 24.

jm/rc (AP, AFP)