There is a vast amount of flesh _ clear and smooth or wrinkled and mottled _ on display in the latest show at Britain's National Portrait Gallery, a retrospective of the work of Lucian Freud.

Freud was the most renowned British portrait painter of the 20th century, and he found that clothes often got in the way.

The artist, who died in July at age 88, approached the human body the way his psychoanalyst grandfather Sigmund Freud approached the mind _ determined to unmask its secrets.

The exhibition, which kicks of with a royal preview for the Duchess of Cambridge on Wednesday, features more than 100 paintings completed over 70 years, many of them nude studies of the artist's friends and family.

Michael Auping, chief curator of the Modern Art Museum of Fort Worth, Texas _ where the show will move after its London run _ said Freud was often asked why he painted so many nudes.

"He would say, every time: 'It's the most complete portrait,'" Auping said.

The exhibition opens with early head-and-shoulders portraits from the 1940s and '50s, then moves on to the to vast, monumental nudes for which Freud became famous. He painted standing up in his London studio, layering oil paint on large canvases with a broad, coarse-haired brush.

Many of the paintings have generic names _ "Naked Solicitor," "Man in a Blue Scarf" _ but the portraits are revealing images of the artist's inner circle, or sometimes Freud himself, often naked and looking vulnerably exposed.

Freud kept his focus on depicting the human body even when the prevailing fashion in art turned to abstraction.

National Portrait Gallery director Sandy Nairne said that for seven decades Freud looked at people with an "unrelenting, determined eye."

"They sometimes feel in your face and very explicitly naked," Nairne said of the paintings. "But that was always with the cooperation of the sitter. In the end, they were sympathetic.

"None of these are casual sitters. They are not figures _ they are individuals."

Berlin-born Freud, who moved to Britain with his family in 1933 when the Nazis came to power in Germany, painted his mother, his brother, his daughters Bella and Esther, and an eclectic array of acquaintances. The subjects of his paintings range from performance artist Leigh Bowery and supermodel Kate Moss to Brig. Andrew Parker-Bowles, a horse-riding friend (who got to keep his uniform on).

He was at work until the very end. The exhibition includes Freud's unfinished final painting, "Portrait of the Hound," which shows his assistant David Dawson and whippet Eli, and appears to have been cut off mid-brushstroke.

Most of Freud's sitters seem to have loved the experience of posing for the master. Sue Tilley, subject of several nudes including "Benefits Supervisor Sleeping" _ which sold at auction in 2008 for $33.6 million, a record for a living artist _ remembers long sessions of chat and laughter.

She said Freud was "a complete one-off ... exciting, interesting, funny and serious _ every single personality trait wrapped up in one person."

"Lucian Freud: Portraits" is open to the public from Thursday until May 27, then moves to Fort Worth from July 1 to Oct. 29.

Auping said he was eager to bring the show to the United States, where the fleshiness of Freud's paintings initially came as a shock.

"We have nothing like this in America," Auping said. "We are the land of Photoshop. We are the land of sleek models. We are the land of no wrinkles.

"It disturbed our sense of abstraction and minimalism. (But) over the years we came to embrace Freud."

British society embraced him, too. Freud gained the ultimate sign of respectability in 2000 when he painted Queen Elizabeth II _ fully clothed. The naturalistic portrait, dubbed daring by some and disrespectful by others, is not on display here.

But the show does have royal approval. The Duchess of Cambridge, wife of Prince William, is a patron of the National Portrait Gallery and attended the show later on Wednesday _ greeting Freud's daughters Bella and Esther Freud.

As she visited, the gallery confirmed the duchess _ formerly Kate Middleton _ will pose for a portrait in the near future, though no decision has been made on which artist will be commissioned.

Tilley said she wasn't worried the duchess would be put off the Freud exhibition by all the flesh on display _ a roomful of it Tilley's.

"I'm not embarrassed about her seeing me naked _ I'm a human being," Tilley said. "I may not be the most gorgeous one under the sun but that's what I am."

"It's art, you know. Poor woman, I'm sure she's seen things before," she said.

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National Portrait Gallery: http://www.npg.org.uk/

Jill Lawless can be reached at: http://twitter.com/JillLawless