How Princess Diana's Glamorous Gown Heading to Auction Showed She Was the 'People's Princess'

The Princess of Wales had a classic reaction when met a fellow partygoer in the same outfit at Windsor Castle

Princess Diana continues to reign as a fashion icon, and a gown that exemplified her exceptional style will soon be available for sale.

Early Thursday, Sotheby’s announced that a black and white strapless Murray Arbeid gown that the late Princess of Wales wore twice in 1985 will be included in its inaugural Fashion Icons auction, opening next week. Princess Diana first wore the timeless style to the Midsummer Night's Ball held in honor of Prince Edward’s 21st birthday at Windsor Castle — and was ever gracious when she met another guest in the same outfit!

According to Vogue, partygoer Natasha Fairweather also wore the taffeta number by the British brand and approached the princess to see how she’d react.

“When I noticed that Diana and [Prince] Charles had gone to the dance floor, I went and danced very close to them so that they would notice. As I remember it, Charles pointed it out to her and she laughed; it certainly wasn’t a big deal,” Fairweather said of the royal repeat in June 1985.

Related: Princess Diana's Original Black Sheep Sweater Is Going Up for Auction: All About the Rare Sale

Cynthia Houlton, Sotheby’s Global Head of Fashion and Accessories, exclusively tells PEOPLE that the interesting twist is that the Princess of Wales reached for the Murray Arbeid dress again soon after. Diana sported the look for the Worshipful Company of Fanmakers Banquet at Mansion House that December, styling it with sapphire and diamond earrings, a statement sapphire, diamond and pearl choker (a favorite combination she wore to the White House!), black gloves and a burst of white feathers.

“This was a gown that other people could purchase, but she chose to wear this gown again. I think what's special about it is that most women who buy evening gowns wear them more than once, so there’s this relatable situation where she wore a gown that you could buy retail. Someone else was wearing it [at the party], but she still liked the gown enough that she decided to wear it again,” Houlton tells PEOPLE.

“There are different elements of her supporting British designers, people referred to her as a ‘People's princess.’ She did things that were often relatable, she wasn't just always doing things that only someone in her position could do. That’s what makes this gown specifically special,” the expert says.

While the curve-hugging Murray Arbeid look has moved through auction before, it will be sold alongside another piece from Princess Diana’s closet with more unusual provenance. In June, Sotheby’s announced that the princess’ original red sweater with a much-discussed black sheep motif would headline the Fashion Icons sale during New York Fashion Week.

Nineteen-year-old Lady Diana Spencer famously wore the Warm & Wonderful jumper (British parlance for a pullover) with jeans to then-Prince Charles' polo match in June 1981, one month before their royal wedding.

Related: Princess Diana's Most Glamorous Looks of All Time

The fashion statement put British brand Warm & Wonderful on the map, and designers Sally Muir and Joanna Osborne received a letter from Buckingham Palace a few weeks later. A secretary said Diana had damaged her whimsical jumper and asked if it could be repaired or replaced. A new sweater was sent and the original became forgotten — until Osborne stumbled upon it in storage this winter.

“We looked at all photographs of her wearing it, and we compared the two and we both felt certain that it was the actual one. We just knew because every jumper is different, so it was easy to see. So we called Sotheby's!” Osborne exclusively told PEOPLE.

The letters Buckingham Palace sent to Warm & Wonderful to coordinate the sweater swap are also included in the auction, and Houlton speculates that the “rare, never been-to-market” nature will elevate the allure — and demand.

Online bidding for Princess Diana’s original red sweater opens Aug. 31 and will run to Sept. 14 through Sotheby’s. The jumper is in good company, as one of ten items in Fashion Icons sale attached to modern style icons.

Can't get enough of PEOPLE's Royals coverage? Sign up for our free Royals newsletter to get the latest updates on Kate Middleton, Meghan Markle and more!

In addition to the late Princess of Wales’ Murray Arbeid frock and original sheep sweater, Sotheby’s is also selling Sarah Jessica Parker's Bird of paradise headpiece from Sex and the City: The Movie, Michelle Obama’s vintage Normal Norrell black lace dress from TNT’s “Christmas in Washington” special in 2010, Kate Winslet’s Alexander McQueen for Givenchy evening gown and bolero from the 1998 Academy Awards, where she was nominated for Titanic, and Madonna’s vintage Brussels lace veil from the first Vanity Fair “Icons Issue.”

On what makes the collection cohesive, Houlton tells PEOPLE, “They're all unique, one-of-one pieces that kind speak to the wearer, the time, who that person is, and that's ultimately what our sale is about.”

For more People news, make sure to sign up for our newsletter!

Read the original article on People.