An erotic painting of a cabaret singer by Pablo Picasso with a second picture on the reverse side could bring over $60 million at auction.
Picasso's "The Night Club Singer" from his Blue Period was created in 1901.
A bawdy picture of his dealer, Pere Manach, is on the back. Sotheby's says it was revealed during a 2000 conservation. An inscription indicates it was intended as a gift to Manach.
The seller is billionaire businessman William Koch, who displayed it so it could be seen from both sides.
He's also selling a 1908 "Water Lillies" painting by Claude Monet. It's estimated at $30 million to $50 million.
The paintings will be auctioned at Sotheby's New York Impressionist and Modern Art Evening sale on Nov. 5.
Koch is a 1992 America's Cup winner and brother of conservative donors Charles and David Koch.