Britain's National Portrait Gallery unveiled the first official painting of the Duchess of Cambridge in a public ceremony in London on Friday.

The portrait of Kate Middleton was created by Paul Emsley who won the Gallery's BP Portrait Award competition in 2007.

"The Duchess explained that she would like to be portrayed naturally -- her natural self -- as opposed to her official self," Emsley said in a statement by the National Portrait Gallery.

The process of getting her portrait made started with an initial meeting with the duchess and the painter followed by two sitting sessions. Middleton posed for the portrait in May and June of last year at Emsley's West Country studio as well as at Kensington Palace.

The artist continued in his statement about his interaction with the Duchess.

"She struck me as enormously open and generous and a very warm person," the artist recalled.

The portrait shows the Duchess, who celebrated her 31st birthday on Wednesday, in a somber background with a serious but smiling expression. 

"After initially feeling it was going to be an unsmiling portrait I think it was the right choice in the end to have her smiling -- that is really who she is," Emsley said regarding painting.

The expectant mother and her husband Prince William were reportedly very pleased with how the painting turned out. Middleton saw the portrait on Friday in a private viewing and responded that it was "amazing... brilliant," according to CNN.

While the Duchess may like the piece, art critics disagree that it is a proper portrayal of Middleton.

"Fortunately, the Duchess of Cambridge looks nothing like this in real life," said Robin Simon, editor of the British Art Journal, to The Daily Mail. "I'm really sad to say this is a rotten portrait."