Kate Middleton's portrait photographer reveals she danced during shoot

All three of her portraits will be added to the permanent collection of the National Portrait Gallery, of which the Duchess herself is patron.

Kate Middleton, who usually releases pictures from her gallery for her birthdays, marked her milestone 40th birthday by posing for professional portraits that have left everyone incredibly impressed.

A palace source explained to Mail Online that the three pictures captured different sides of the future Queen. The insider explained, "From the three photographs, you can see the three aspects of Kate's personality. There is the regal side to her – as you can see in the classic shot where she is looking off into the distance; there is the more informal image in the red dress as a modern woman at 40; and then there is the close-up, which offers a more intimate perspective."

Paolo Roversi, the photographer behind the pictures, is now revealing the work that went behind them. He also shared that the Duchess of Cambridge danced during their photoshoot to get the perfect picture to capture her carefree spirit. However, the picture hasn't been released yet and will be "a secret image for now."

He told Corriere.it about the photoshoot at Kew Gardens, "In the end I wanted to take pictures in motion, so with that wonderful wide skirt I made her dance in front of my camera, a kind of accelerated waltz mixed with a pinch of rock'n'roll."

The selection process for the three pictures out of the 250 images they clicked went on several levels. The photographer narrowed them down to 70, before Kate chose a dozen of her favourites. They sat together to select the final three pictures, with a bit of help from her husband and children.

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Kate's husband Prince William and their three children, Prince George, eight, Princess Charlotte, six, and Prince Louis, three, got to choose one of the photographs that were released for the public. They chose the black-and-white image in which Kate is facing the camera, as they believed it captured her as "a carefree girl returning." All three of her portraits will be added to the permanent collection of the National Portrait Gallery, of which the Duchess herself is patron.