An artist from Bradford on Avon has hit the headlines after the first official portrait of the Duchess of Cambridge was unveiled.

Paul Emsley took three and a half months to paint the masterpiece, called HRH The Duchess of Cambridge, using a technique of building thin layers of oil and glazes on canvas.

The portrait is going on show at London's National Portrait Gallery, which commissioned the work. The duchess is the gallery's patron, and Mr Emsley was chosen to paint the portrait by the gallery's director, Sandy Nairne.

Mr Emsley, 64, originally planned to produce an unsmiling portrait, but upon meeting Catherine he changed his mind. He said the Duchess had expressed a desire to be portrayed as her natural self, rather than her official self.

“It was the right choice in the end to have her smiling. That's really who she is.

"Everyone, I think, recognises her partly through her lovely hair and I have altered the colour of the eyes slightly to match the colour of the blouse and the blue background.

The Duchess sat for the artist in his Bradford on Avon studio in May and at Kensington Palace in June.

Mr Emsley worked from a series of photographs he took of Catherine, which he said was easier.

“I am always worried about the sitter. Are they cold, are they hot, are they comfortable?

"Photography today is so accurate and so good that it's really so much easier just to take photographs and work from them."

The portrait, which has received a mixed reaction from the art world, will be displayed as part of the National Portrait Gallery's Contemporary Collections in London and was presented to the gallery's trustees in November.

The artist described his work as simple and said: "I don't have lots of things in the background. I like large faces; I find them strong and contemporary. I am interested in the landscape of the face, the way in which light and shadow fall across the forms. That is really my subject matter. To have anything else in there is really just an interference."

Art Fund director Stephen Deuchar said: "The unveiling of a first official portrait of a royal sitter is always an important and intriguing moment, defining and enshrining their public image in a new way."

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