With an exhibition of her fashion announced to commemorate the 20th anniversary of her death next year, Princess Diana's style has been back on the agenda lately. On Monday, three prom dresses owned and worn by the Princess will be going up for sale through vintage fashion auctioneer Kerry Taylor, each one offering a renewed insight into the life and style of a woman who remains an enduring fashion icon for women of all ages.

The dress which symbolises a carefree moment

The first lot is a brown tartan day dress with a starched white Peter Pan collar, which Diana wore Braemar Highland Games on 4th September 1982. "This dress was worn a year after Charles and Diana married and it was such a happy and relaxed moment," Kerry Taylor tells The Telegraph of the item. "We see her laughing with the Queen in that dress. It's part of a happy interlude - the calm before the storm." Designed by Caroline Charles, this was a bespoke design for the Princess and symbolises the careful thought which she put into everything she wore, giving a clever (and fun, let's not forget) sartorial nod to the occasion.

Princess Diana in a Caroline Charles dress in Scotland in September 1982 CREDIT: GETTY

Another piece being auctioned is a vibrant turquoise silk suit made for Diana by her favourite designer Catherine Walker for her tour to Australia and New Zealand in April 1983. "She was photographed wearing this ensemble rubbing noses - the traditional Maori greeting," Taylor explains. "It formed part of a large group order the Princess had made to Catherine Walker, in whom she had enormous faith – so much so that she didn’t even ask to see provisional sketches and trusted her to select and make the dress directly."

Princess Diana meeting Maoris in New Zealand CREDIT: REX

The mother and daughter who stumbled upon Diana's dresses in a second hand shop

The dresses are evidence of the way Diana's wardrobe is now spread across the world. When she was alive she would give clothes to friends or donate them to charity and second-hand shops, but she also sold many of her more famous pieces at Christie's in 1997, raising $3.25 million for charity in the process.

Both the tartan and turquoise dresses are being sold by a private mother and daughter who first purchased the pieces in a 'posh second-hand shop' where they were simply searching for good value outfits to wear themselves. It was through "whispers" that they discovered that the dresses they were interested in had belonged to the Princess.

The turquoise silk ensemble which once belonged to Princess Daina CREDIT: KERRY TAYLOR AUCTIONS/ THE SALE ROOM

"The turquoise dress has quite a low estimate simply because the lady who bought it, actually wore it," says Taylor. "She had it altered and she wore it to a wedding where champagne spilled down the front - if it weren't for that, we would be estimating £6,000 rather than £600." The checked dress is expected to fetch between £6,000 and £9,000 because the daughter who bought "has a very similar figure to Diana's so it hasn't been changed, although it has been worn."

Diana wearing the checked dress which will now appear in a new exhibition at Kensington Palace

These weren't the only items purchased by the duo. Earlier this year, Taylor auctioned a checked Emanuel Couture dress which Diana wore in Venice. "It had been taken there I am told by Sarah Ferguson's mother, who was taking clothes that Diana and Fergie no longer wanted, and that's how it came to my client," Taylor told The Telegraph at the time.

That dress was eventually bought at the auction by Historic Royal Palaces who will be exhibiting it as part of their Diana: Her Fashion Story exhibition which will open at Kensington Palace in February 2017. So could the palace be among those looking to bid on these newly available outfits?

The velvet gown which highlighted Diana's most elegant features

The final Diana dress in the auction is a crushed velvet gown created for Diana by Bruce Oldfield which she wore to attend a dinner given by then Portugese president Mario Soares at the Ajuda Palace in Lisbon during a visit to Portugal with Prince Charles in February 1987.

The Bruce Oldfield gown highlighted Diana's long neck

"The velvet gown was part of the 1997 Christie's auction," says Taylor. "The off-shoulder design by Bruce Oldfield really highlighted Diana's beautiful long neck. With the overskirt's 18th century shape and the purple embossed velvet, it's very regal. It has this inner pencil skirt so that when she walked it showed a glimpse of leg. Seeing it on the mannequin doesn't quite show that quality. The dress hasn't been worn since Diana wore it so it is special in that way." Taylor estimates that it could sell for up to £70,000.

According to a piece published in the New York Times at the time of the 1997 auction, the prom dresses uk was bought by Donna Coffin, the wife of a Chicago computer consultant, who paid $26,450. "Mrs. Coffin said that she did not know what she would do with her purchase, but that she had ''a lot of respect and admiration' for Diana," according to the article.

"The people looking to buy at these auctions aren't doing it for the fashion but for the Princess alone," says Taylor. "When you think of James Dean, Marilyn Monroe and even Diana, they are these personalities who were beautiful and died young. There's the sense of tragedy about a life cut short, the romance of unfinished business. The fact they will never grow old or have a bad hair day adds to the specialness."

The auction will take place on Monday at Kerry Taylor auctions and through The Saleroom