AS one of the most photographed and glamorous women in the world, the Duchess of Cambridge wanted to show off a more relaxed and intimate side in her first official portrait.

And while the newest member of the Royal Family – and her husband – are said to be thrilled with the results, the portrait, by Glasgow-born painter Paul Emsley, has divided opinion in the art world, with the work derided as "rotten, dour and pretty ordinary" by some critics.

The larger than life-size work, which depicts the Duchess with a faint smile and a soft demeanour, was unveiled to the Duchess at a private viewing at the National Portrait Gallery, where she enjoyed the first glimpse of the work with the Duke of Cambridge.

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Afterwards, she told Emsley: "It's just amazing, I thought it was brilliant," while the Duke described it as "absolutely beautiful".

She was seen shaking hands with Emsley. who was commissioned by the National Portrait Gallery and was chosen by its director Sandy Nairne following a selection process which involved the Duchess.

While the painter has been praised for his informal approach to his subject, its reception in some corners of the art world has been far from enthusiastic. Robin Simon, editor of the British Art Journal, said: "Fortunately, the Duchess of Cambridge looks nothing like this in real life. I'm really sad to say this is a rotten portrait.'

Art critic Waldemar Januszczak said he was "disappointed" by the portrait and that there was a lack of sparkle in Kate's eyes.

"I was disappointed, to be honest. I have been waiting for it, like everybody else, with great expectation because the Duchess of Cambridge is someone who we know likes art and was presumably going to be an enlightened patron.

"But I think she's been let down really by the picture."

Emsley, 65, who spent a large part of his life in South Africa but who has now returned to the UK, is the 2007 winner of the Gallery's BP Portrait Award competition and is known for his detailed, almost photographic, portraits which include every hair and pore of the sitter.

His subjects include Nelson Mandela and the author VS Naipaul.

Richard Stone, Britain's most prolific royal portrait artist, said the work had captured Kate's evident warmth and approachability. He said: "I liked it, very much so. So often with official portraits they can be rather stiff and starchy, but this has a lovely informality about it, and a warmth to it."

Emsley, 65, said after the unveiling: "I was delighted to get the commission and then after that it began to sink in to me how important this would be.

"A person whose image is so pervasive, for an artist it is really difficult to go beyond that and find something original – you have to rely on your technique and your artistic instincts to do that and I hope I've succeeded."