A woman who posed naked for British artist Lucian Freud revealed Saturday she was paid 20 pounds -- and the resulting painting is expected to become the most expensive work by a living artist.

Sue Tilley said she had been delighted to be the inspiration for "Benefits Supervisor Sleeping" in 1995, which is set to become the most expensive painting by a living artist when it is sold in New York next month.

Art experts expect the painting of a fleshy woman reclining on a sofa to fetch up to 17 million pounds (33.5 million dollars, 21 million euros) when it goes under the hammer in New York in May.

Tilley, nicknamed Big Sue, joked she was the first nude pin-up to grace the front page of the Financial Times newspaper, which carried a photograph of the painting Saturday.

"I can't quite believe it, to be honest," she told the BBC.

"I only found out on Thursday afternoon. You know, I didn't have any idea it was going to happen, so I'm a bit in shock.

"I was reading on the Internet... all the things about it. And I was just going 'Oh my god', I could hardly believe it was about me.

"Half the time I don't really think it's me. But then this morning I was looking at it again and I was going: 'that's my funny little face!'"

Tilley, who now manages a job centre in London, said she was introduced to Freud by a friend and became his muse, often going for lunch with the artist before posing.

Freud, the 85-year-old grandson of pioneering psychoanalyst Sigmund Freud, was born in Berlin but his family fled Germany as the Nazis rose to power and he became a British citizen.

He has said: "I paint people, not because of what they are like, not exactly in spite of what they are like, but how they happen to be."