A painting by Austrian expressionist Egon Schiele, which went missing after it was stolen by the Nazis in 1938, could fetch up to £6m at auction.
Wilted Sunflowers, or Autumn Sun, which was confiscated from Austrian art dealer Karl Grunwald, will be sold by auction house Christie's on 20 June.
An anonymous collector asked Christie's to value the painting, which dates from around 1914, last year.
The owner returned the work to Mr Grunwald's family, who are selling it.
Mr Grunwald, who bought the painting some time between 1917 and 1937, is said to have stopped the artist going to the frontline in World War I.
The art dealer helped the painter to become appointed war artist instead.
When Hitler annexed Austria in 1938, Mr Grunwald fled Vienna for Paris but his collection was confiscated by the Nazis in Strasbourg.
In 1942, the collection was auctioned by the Nazi regime.
Mr Grunwald's wife and daughter died in a concentration camp during the war and he spent the rest of his life searching for his former possessions.
Mr Grunwald's son, Frederic, took up the search on his father's death.
When he died two years ago, aged 85, one of his last messages to his family was to not forget the Sunflowers painting.
The watercolour and oil painting is said to depict Schiele's sombre mood on the eve of the World War I.
Schiele pays homage to Vincent Van Gogh's famous image of sunflowers in the painting, which is thought to have been in France since 1938.
Jussi Pylkkanen, president of Christie's Europe, said: "It's not overstating it to say this is a masterpiece that would grace any great institution.
The Grunwald family attended the painting's London unveiling
"The owner of the picture had no idea that there was a restitution link with this picture."
Mr Grunwald's granddaughter Cory Pollack said the family's "biggest fear" had been "that it was destroyed or lost".
She said: "So many bad things happened to the family during the war and we feel that this is part of the healing process.
"It was very emotional when we heard about it. We all were just overwhelmed."
The painting will be auctioned as part of an impressionist and modern art sale in London.