Freud's latest super model

He is hailed as Britain's greatest living artist and she is Britain's most celebrated beauty.

Now their collaboration, Lucian Freud's portrait of a naked and pregnant Kate Moss, is set to fetch up to £3.5million at auction.

The near-lifesize, full-length study of the normally waif-like Moss, entitled Naked Portrait 2002, is unveiled at Christie's today before going under the hammer at a sale early next year.

Ms Moss is, with the exception of the Queen, probably the most famous figure to be painted by Freud, grandson of the legendary psychiatrist Sigmund Freud.

Freud, now 81, is said to have been reading the fashion magazine Dazed And Confused, then edited by Ms Moss's boyfriend Jefferson Hack, and read that one of her ambitions was to be painted by him. As she was pregnant, she was happy for protracted sittings and, unlike fellow model Jerry Hall, Ms Moss kept all of her appointments.

The result of the strangely appropriate collaboration is a strong and accomplished work.

For Freud, the portrait presented a major challenge because he prefers to paint people he knows well and who are not professional models. Well versed at holding poses, models are too often "hardened", according to Freud. "They've grown another skin because they've been looked at so much," he said at the time.

"Part of liking to work with them naked is that I can see more: see the forms repeating right through the body and often in the head as well."

Freud began the portrait in 2001. The result was that the slight and slender model is presented as an imposing physical presence. The model's face, which tends to dominate, is overshadowed.

Works by Freud are rare and highly sought-after. Current world best for a Freud is £5.8 million, paid at Sotheby's in New York in 1998 for Large Interior W11, although the Kate Moss portrait may challenge that record.

Christie's specialist Fernando Mignoni said today: "In this portrait, the slow scrutiny of the Old Masters meets the world of contemporary fashion, fleeting magazine covers and commercial advertising." Naked Portrait 2002 is being offered for sale at Christie's on 9 February.