A 1963 female nude by Francis Bacon may raise as much as $30 million at an auction next month.

Bacon’s sexually charged “Portrait of Henrietta Moraes,” showing one of his favorite models sprawled across a bed, has a formally undisclosed estimate of about 18 million pounds at Christie’s International (CHRS) in its Feb. 14. London sale.

The painting’s owner, an unidentified New York collector, is testing the market for high-value contemporary works. Bacon is the U.K.’s most expensive artist at auction. The portrait has never appeared at public sale before and has no guaranteed minimum price, said Christie’s. It dates from the year that the painter embarked on his relationship with George Dyer.

“Bacon’s lack of personal erotic interest in naked females did nothing to prevent these paintings from being as passionate as those of the male bodies that obsessed him,” said David Sylvester, a U.K.-based art critic, who interviewed the artist in the 1960s and 1970s.

Moraes was a close friend of Bacon’s during the 1950s and 1960s. Like Bacon and Lucian Freud, she was a regular visitor to the Colony Club Room in Soho. She battled drink and drug addictions, had many lovers, once shared an apartment with singer Marianne Faithfull and was sent to prison after an unsuccessful attempt to become a cat burglar. She appears in a number of paintings using photos taken of her by John Deakin.