The first official portrait of Britain’s Kate Middleton was unveiled at the National Portrait gallery in London on Friday, with the Duchess of Cambridge describing it as “just amazing”.

The portrait was painted by award-winning artist Paul Emsley and took several months using a technique of building thin layers of oil and glazes on canvas.

The 31-year-old royal, whose pregnancy was announced last month, sat for the artist in May 2012 at his studio, and again in June at Kensington Palace. Emsley said he wanted to capture Kate’s natural beauty.

The artist said he was originally going to paint her without a smile, but changed his mind shortly after meeting her.

The portrait — called HRH The Duchess of Cambridge — shows the mother-to-be against a dark background with her lips pursed into a wry smile.

“I think it was the right choice in the end to have her smiling. That’s really who she is, I think,” Emsley was quoted as saying by BBC.

The 65-year-old artist also knew he wanted to make a feature of Kate’s hair. “Everyone, I think, recognises her partly through her lovely hair,” he said.

The painting took three-and-a-half months to complete and was presented to the portrait gallery’s trustees in November.

Kate and her husband Prince William visited the Gallery on Friday for the unveiling. Kate thanked Emsley, saying: “It’s just amazing, I thought it was brilliant.”

Prince William also had high praise for the painting, saying: “It’s beautiful, it’s absolutely beautiful.”

The portrait will be displayed as part of the National Portrait Gallery’s Contemporary Collections.

The artist’s other subjects have included former South African President Nelson Mandela and Indian-origin author V.S. Naipaul. In 2007, he won the BP Portrait Award for his depiction of fellow artist, Michael Simpson.

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