Portrait of Elisabeth Lederer is now the most expensive work of modern art ever sold at auction. How did Sotheby’s pull off the impossible? Who, more importantly, bought it?

A self-portrait by Frida Kahlo has a chance of setting a record for a female artist when it goes on sale, also at Sotheby's in New York. Estimated at $40 to $60 million, the 1940 piece called 'The Dream (The Bed)' shows the Mexican painter sleeping in a bed overshadowed by a large skeleton.

At $236.4 million, a portrait by Gustav Klimt is the second most expensive painting sold at auction, while Maurizio Cattelan’s golden toilet drew $12.1 million.