CNN- News- A picture of an overweight woman lying naked on a couch, painted by the British artist Lucian Freud, is expected to set a record for any work by a living artist when it goes up for auction Tuesday night.

1 of 2 Christie's auction house in New York expects the life-size 1995 portrait to sell for between $25 million and $35 million.

Christie's calls it a bold and imposing example of the stark power of Lucian Freud's realism, depicting the forceful and undeniable physical presence of people and things.

Tilley, now 51, told CNN she was initially embarrassed to pose naked for the artist but they soon grew comfortable in the studio -- so comfortable, in fact, that she confessed to falling asleep while posing.

The painting challenges modern notions of beauty and elicits a reaction from everyone who sees it.

Freud, 85, has been described as Britain's greatest living realist painter. He is the grandson of psychoanalyst Sigmund Freud and came to London from Germany when he was a child.