Unseen image shows Kate Middleton taking picture of boyfriend Prince William at 2006 Sandhurst polo match – four months before she made first official outing alongside the Royal Family at passing out parade

An unseen image of Kate Middleton with Prince William at a polo match in Sandhurst, four months before she officially joined the royal family, has been revealed by a designer who befriended his late mother, Princess Diana.

The photo was taken by American couturier and bridal wear designer Pat Kerr Tigrett on July 13, 2006, after she received an invitation to watch the charity match.

It shows William, then 24, on horseback in polo attire at the Royal Military Academy Sandhurst, in Berkshire, as his girlfriend of three years takes a photo of him.

In December that year, Kate – now the Princess of Wales – joined Queen Elizabeth II, Prince Philip and the then Prince Charles at William’s passing out parade at Sandhurst.

She beamed alongside her parents Carole and Michael, wearing a scarlet coat and black hat that matched the colors of William’s uniform.

The official appearance was billed as the strongest sign yet that the couple would marry, but they split in April 2007.

Royal fans were bereft, but were soon given a boost when the couple reunited a few months later and then got married in 2011.

Ms Tigrett is seen in another recently revealed image posing next to Prince William – who she says gave her his trophy – during a day out in Sandhurst.

Ms Tigrett is seen in another recently revealed image posing next to Prince William – who she says gave her his trophy – during a day out in Sandhurst

The designer revealed the images in an interview with MailOnline on the occasion of the sale of three dresses from the late Princess Diana.

Mrs Tigrett is selling them almost 30 years after she bought the garments at the famous Christie’s auction in June 1997, where Diana sold 79 of her evening dresses to raise money for charity.

The designer said of the visit to Sandhurst: “This lovely invitation came from Prince William to attend a polo match in Sandhurst,” she smiles.

‘This beautiful girl took pictures of him and it seems that Catherine and the prince knew each other.

‘It was a wonderful occasion and of course Prince William won. He then entered the VIP tent with his trophy in hand.

‘We had such a lovely chat about his mother and her childhood home Althorp. To my surprise, he presented me with his trophy, which I truly cherish.”

Mrs Tigrett first met Diana in 1984 when she lived in London’s Regent’s Park with her husband John Tigrett, a Tennessee entrepreneur.

In December 2006, Kate joined Queen Elizabeth II, Prince Philip and then-Prince Charles at William’s passing out parade in Sandhurst. It was her first official appearance alongside the royal family. Above: Kate sits next to her mother Carole and father’s friends Michael and William

Kate walks between her mother and father during William’s passing out parade at Sandringham in December 2006

Queen Elizabeth II enjoys a funny moment with her grandson Prince William as she observes him during his passing out parade in Sandhurst

She met the princess at the home of financier Sir James Goldsmith and his third wife Lady Annabel.

‘When I first met Princess Diana, she was with Prince William. It was before Harry was born,” she said.

‘I thought, ‘How young she is, how young to take on such an incredibly impossible responsibility as the future Queen of England.’

“But she was incredibly charming and she was so much fun and she loved her boys.”

Their paths crossed over the next 13 years as they attended balls and events together.

Mrs Tigrett paid a total of £80,241 for four of Diana’s dresses: a midnight blue tulle ballerina dress by Murray Arbeid; a magenta silk and lace dress by Victor Edelstein; a cream-colored silk dress from Catherine Walker and a black velvet dress from Catherine Walker with a lace collar.

The car pass for the July 2006 charity polo match at Sandhurst Royal Military Academy

American couturier and bridal fashion designer Pat Kerr Tigrett (pictured above in 2017). She bought four of Diana’s dresses at Christie’s famous auction in 1997. The couple had known each other since 1984

She now sells everything except Catherine Walker’s black velvet dress.

The garments will be sold on June 27 through Julien’s auction house in Los Angeles.

Diana died in a car accident in Paris at the end of August 1997.

Mrs Tigrett said: ‘The phones were ringing like crazy, and I just cried. It was so terrible. She was so loved by so many and those children of hers were her life.

“When she died, I literally put my dresses away.”

The following year, Mrs Tigrett was invited by Diana’s sister Lady Sarah McCorquodale to make a documentary about Diana’s wardrobe.

The film would accompany the exhibition Diana: A Celebration, which was held at the Princess’s ancestral home, Althorp Park, in aid of the Diana, Princess of Wales Memorial Fund.

Mrs Tigrett said she was taken to Althorp where she was shown Diana’s wedding dress and her grave, which is on a small island on the estate.

“I felt so blessed to be able to say goodbye,” she said. “I took pictures of where she was buried, thought about her, prayed for her and read all the beautiful messages her family had written.”