In the snaps, the future Queen Consort wears different Alexander McQueen dresses with her hair loose around her shoulders. They were taken at Kew Gardens in November by fashion photographer Paolo Roversi.

       Mr Roversi described photographing Kate as "a moment of pure joy" and said with her "positive energy" she can "bring hope to the whole world".

       He 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.

       "It was a profound and rich experience for me, an unforgettable moment.

       "I have met a wonderful person, a person who, with her positive energy, can bring hope to the whole world."

       Kate has been pictured in three relaxed poses.

       The images will enter the permanent collection of the National Portrait Gallery, of which The Duchess is Patron.

       In one, Kate is seen wearing a one-shouldered red McQueen dress accessorised with earrings from the Queen’s private collection.

       READ MORE: Royal fans gush over stunning Kate pictures ahead of 40th birthday

       She smiles at the camera, with her hands nestled in the pockets of the gown.

       The photographer, who has shot the likes of Naomi Campbell and Kate Moss, is renowned for adventurous film and printing techniques.

       As a result, the two other images released for the occasion have been produced in monochrome, giving them an ethereal quality.

       One of these, shows the Duchess with her hair swept over her shoulder as she smiles at the camera.

       Kate is expressionless, gazing to the left in another.

       Her engagement ring, which belonged to Diana, Princess of Wales, is on display.

       The ring features a 12 carat Ceylon sapphire, originating from Sri Lanka.

       The Duchess also wears earrings which belonged to Diana.

       Kate is expected to mark her birthday on Sunday, January 9 with a private family affair at the Cambridges' home in Norfolk.

       Her husband, Prince William, will celebrate turning 40 in June.

       Typically, senior members of the Royal Family release pictures to mark key dates.

       Last year, Kate’s birthday was not marked with a new photograph as it occurred amid a Covid enforced lockdown.

       Instead, a photo of Kate during a royal engagement was released alongside a sombre message of thanks.

       It read: "Thank you for your kind wishes on The Duchess’ birthday.

       "Birthdays have been very different in recent months, and our thoughts continue to be with all those working on the front line at this hugely challenging time."