London, UK - Duchess Kate, style icon of the British royal family, celebrated her 40th birthday on Sunday, and the palace released three new portraits to mark the occasion.

Kate has been pictured in three relaxed poses, wearing different Alexander McQueen dresses and with her hair flowing.

Celebrated fashion photographer Paolo Roversi, famed for working with industry stars like Naomi Campbell and Kate Moss, described photographing the duchess as "a moment of pure joy" and said with her "positive energy" she can "bring hope to the whole world."

The duchess will celebrate her 40th birthday on Sunday, and the event is likely to be a private family affair marked at the Cambridges' home in Norfolk, England.

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The birthday heralds the start of an important decade for the monarchy and the future queen, who will be at William's side as events progress, watching her young family grow up and pursuing her own charitable interests.

Roversi said: "Taking the portrait of Her Royal Highness the Duchess of Cambridge was a true honour for me and a moment of pure joy."

"I was moved by her warmth and friendly welcome and enchanted by her shining eyes that reflected the loveliness of her soul and her smile showing the generosity of her heart."

In one image, Kate wears a striking red McQueen dress and earrings loaned by Queen Elizabeth II and beams at the camera as she appears to have her hands casually in the gown's pockets.

Roversi is known for his adventurous film and printing techniques, and the remaining images have been produced in monochrome that give them an ethereal quality.

In one, a head and shoulders image, the duchess smiles broadly, and in the other, with her engagement ring prominently on display, Kate is shown in profile and looking left.

She wears earrings that belonged to Diana, Princess of Wales, in both photographs.