The 'awful' moments after Diana's death, polo with William and unseen pictures of the Prince and Kate: Designer who befriended the Princess tells all as she puts three of the royal's dresses up for sale (and they could fetch up to £1million)

Stepping out of a chauffeur-driven Jaguar into the balmy warmth of a summer's evening, Princess Diana smiled briefly for photographers as she walked into London's Dorchester hotel for a charity fundraiser hosted by former cricketer Imran Khan and his wife Jemima.

It was Independence Day, 1996, and Diana betrayed no hint of what had happened just an hour earlier: at 6.30pm the then Prince Charles' solicitors Farrer and Co had delivered an offer for a divorce settlement to the London officers of her advisers Mishcon de Reya.

Instead, the Princess, who described herself as 'Queen of Hearts' in her notorious BBC Panorama interview, was confidently looking to the future, as confirmed by one of the fundraiser's most generous guests - American couturier and bridalwear designer Pat Kerr Tigrett.

In fact, Diana was planning what would become a famous charity auction of her evening gowns at Christie's, in New York, along with a trip to Memphis, Tennessee, to visit the St Jude Children's Research Hospital and take a tour of Elvis Presley's Graceland Mansion.

Pat, who is on the board of the hospital, bought four of Diana's dresses at the Christie's auction and became a friend of the late princess.

'I was talking to her about the hospital,' she says. 'She already knew about St Jude and was very involved in the charity, so I invited her to come to Memphis and see the hospital for herself.

'Her eyes just lit up and she said: "I would love to do just that. I could bring the boys [Princes William and Harry] with me."

Pat is now selling three of Diana's dresses via Julien's auction house in Los Angeles and they could raise up to £1million – not bad for an £80,000 investment.

Diana, Princess of Wales, wearing a strapless blue dress designed by Murray Arbeid and long, pink gloves, attends the premiere of Andrew Lloyd Webber's 'Phantom of the Opera' at Her Majesty's Theatre on October 9, 1986 in London. The dress is tipped to sell for up to $400,000 when it goes on sale in Los Angeles on Thursday

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

'I was so excited,' continues Pat of Diana's planned visit to Memphis.

'I was planning to take them to Graceland, which she would have loved, and to introduce them to Priscilla Presley - she and Elvis were great friends of mine - but tragically it was too late. Life is so fragile.'

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Pat, who describes herself as an 'Anglophile', first met Diana in 1984 when she lived in London's Regent's Park with her husband John Tigrett, a Tennessee entrepreneur.

He was a business partner of the late financier Sir James Goldsmith, who was then married to his third wife Lady Annabel Goldsmith.

Lady Annabel was mother of his three children Jemima, Zac and Ben, and the family often socialised with Pat and her husband.

Annabel was equally close to Diana – she was once described as a 'second mother' to the Princess – so it was inevitable that Pat and Diana would eventually meet.

The occasion came when Annabel invited the couple, and their five-year-old son Harrison, to Sunday lunch at the family home - Ormeley Lodge near Richmond Park -  and Diana, 23, was there with Prince William, then a toddler.

An unseen image of Kate Middleton taking a picture of her boyfriend Prince William on horseback and dressed in his polo gear at Sandhurst, July 2006. Pat Tigrett, who took the image, said: 'This beautiful girl was taking photographs of him, and it appears that Catherine and the Prince knew each other.' The image was taken four months before Kate made her first official public appearance alongside the Royal Family at William's passing out parade at Sandhurst

Prince William with Pat Ker Tigrett at a charity polo match at Sandhurst, July 13, 2006

Pat received an invitation in the post from Prince William, who was doing his training at the Royal Military Academy in Sandhurst

'When I first met Princess Diana, she was with Prince William. It was before Harry was born. I thought: "How young she is, how young to be taking on such an incredibly impossible responsibility as the future Queen of England".

'But she was totally charming and was such fun and she adored her boys.'

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

Pat is a collector of antique lace, textiles and memorabilia, and owns more than 1,000 pieces, including a handkerchief belonging to Charles I, a Queen Anne purse and an album of photographs of the Duke and Duchess of Windsor's wedding, and was a regular at London's auction houses Christie's, Bonham's, Sotheby's and Philips.

So, the designer, known as the 'Lace Lady' in the States, was on the guest list for one of the most anticipated auctions of the 20th century, when Diana, inspired by Prince William, put up for auction 79 of her evening gowns to raise money for the Royal Marsden Hospital Cancer Fund and the AIDS Crisis Trust.

Pat and her husband were invited to the £150-a-ticket gala in New York, on June 23, 1997, when Diana, clad in a pink-and-blue floral beaded Catherine Walker cocktail dress, made two circuits of the crowded hall, signing catalogues, greeting guests, and saying farewell to her dresses, which were displayed on mannequins in an 'English country garden' setting, complete with real geraniums.

And they were in the front row two days later when 1,100 people crammed into Christie's Park Avenue auction house in Manhattan, to bid for a moment in history. While museums, fashion connoisseurs, haute couture collectors and Diana fans leafed through the glossy catalogues, cheers went up for the successful bidders.

Pat bought four dresses at the auction, paying a total of £80,241: a Murray Arbeid midnight blue ballerina-length tulle gown embroidered with diamanté stars, for which she bid £29,053; a £15,218 Victor Edelstein magenta silk and lace dress, which had a flounced skirt; a £21,444 cream silk Catherine Walker dress, embroidered with a flight of gold and silver sequinned falcons on the bodice and the train; and a £14,526 black velvet Catherine Walker gown with a lace collar.

Afterwards, she told TV hosts Larry King and Joan Rivers: 'I bought tonight for a different reason than the majority of buyers that were there because I'm a serious collector of antique textiles and also historical Royal textiles and Royal memorabilia.

'I'm also a fashion designer and it just seemed the right thing to do. It is a part of history.'

However, just two months later, Diana was tragically killed in a car accident in Paris, and her dresses went into storage. 'I was at the University of Virginia taking Harrison back to college with some friends,' she recalls. 'We all had been for dinner and when we got back to our hotels, I flipped on the TV and found out. I was horrified.

'I will never forget the language of the presenter speaking from London. You could tell it was difficult for him to explain she had gone.

'The phones were ringing like crazy, and I just cried. It was so awful. She was so well loved by so many and those children of hers were her life. The minute she died, I literally put my gowns away.'

However, Diana's death was not the end of Pat's connection with the Royal Family. The following year, she received a phone call from the Princess's sister Lady Sarah McCorquodale, asking if she would fly over to Britain, from Memphis, to make a documentary about Diana's wardrobe.

Princess Diana in Hamburg, Germany, in 1987 wearing a black silk lace off-the-shoulder gown by Victor Edelstein layered over deep magenta silk. The dress is expected to sell for up to $400,000

Diana wearing Murray Arbeid's ballerina-length midnight blue strapless dress adorned with diamanté stars for a ball hosted by King Constantine of Greece at the The late designer Murray Arbeid got his wrists slapped by the Queen of Jordan when Diana wore his ballerina-length midnight blue strapless dress, adorned with diamanté stars, for a spectacular ball hosted by King Constantine of Greece on 12 July 1986. The dress is tipped to sell for up to $400,000

The film was to 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.

'I had just left London,' she explains, 'But Diana's sister Sarah called me and said they really wanted me. So, I just jumped on a plane and rolled back in.

'I flew in the day beforehand and then a driver picked me up at the Covent Garden Hotel at 6am and drove me to Althorp in the pouring rain.

'We got there about 8.30am, drove through these magnificent gates, to the stables on the left-hand side of the house, which is where the museum was.

'The film crew was waiting for me and interviewed me. I was the only person in the museum apart from them, so I got a really good chance to look at the 28 outfits being exhibited including the famous landmine outfit. It was remarkable.

'As a bridal designer, I will never forget the thrill of seeing her wedding gown and the bridesmaids' dresses.

'This was the most famous wedding gown in modern history, for Diana's wedding to Charles, Prince of Wales, and I was so excited to be there because I'm so into weddings. I have been all my life really.

'Afterwards I walked round the grounds at the back of Althorp and visited her grave on the island.

'I felt so blessed to be able to say goodbye. I took photographs of where she was buried, thought about her, prayed for her and read all the wonderful messages written by her family.'

Then, eight years later, she received an invitation in the post from Prince William, who was doing his training at the Royal Military Academy in Sandhurst.

Pat at Kensington Palace's Sunken Garden, where a statue of Princess Diana was unveiled by Prince William and Harry in 2021

Pat Kerr Tigrett with her husband John and former US President Ronald Reagan

Pat Kerr Tigrett with Priscilla Presley (right). She had planned for Diana to meet Priscilla

William was playing in a charity polo match at Sandurst on July 13, 2006.

'This lovely invitation arrived from Prince William to attend a polo match at Sandhurst,' she smiles.

'This beautiful girl was taking photographs of him, and it appears that Catherine and the Prince knew each other.

'It was a wonderful occasion and, of course, Prince William won. He then entered the VIP marquee holding his trophy.

'We had such a nice conversation about his mother and her ancestral home Althorp. To my surprise he handed me his trophy which I truly cherish.'

Pat's dresses remained in storage until 2013 when she was contacted by curators at Kensington Palace, who were organising the exhibition of Diana's gowns, entitled Fashion Rules. She loaned them her Murray Arbeid dress for the 2013 show and its follow-up Fashion Rules Restyled.

Then, in 2017, she lent the gallery her Victor Edelstein gown and the Catherine Walker cream dress that Diana wore to Saudi Arabia with the falcons, a symbol of the ruling House.

In the June 27 sale in Los Angeles, Pat is also selling a photograph album which belonged to the Duke of Windsor, an oil painting of Windsor Castle, Charles I’s handkerchief and 'I've really enjoyed owning them,' she explains. 'But it's time for someone else to have them.'

Princess Diana's Elegance and a Royal Collection is at Julien's Auctions on June 27.

Claudia Joseph is the author of Diana: A Life in Dresses, £40 at ACC Art Books.