Princess Diana’s iconic black dress, famously dubbed her “revenge dress”, is set to go under the hammer for the first time in nearly three decades.

The late Princess of Wales wore the strapless black silk dress to a fundraising event at London’s Serpentine Gallery in 1994, shortly after a television documentary aired in which her then-husband, Prince Charles, admitted to being unfaithful during their marriage.

Her appearance in the dress became one of the most memorable moments in royal and popular culture.

Sotheby’s expects the dress to fetch up to £220,000 ($300,000) when it is auctioned on 9 December.

It was last sold at auction in 1997, when Diana put 79 of her dresses up for sale to raise money for charity, just months before her death.

Morgane Halimi, Sotheby’s global head of handbags and fashion, said Diana understood that fashion could be used as a form of communication.

“On her own terms, Princess Diana turned the dress into one of the most powerful messages she ever made,” she said.

Diana’s appearance at the Serpentine Gallery came on the same evening that a documentary aired in which Prince Charles, now King Charles III, publicly admitted his infidelity.

Although details of the interview had been leaked days earlier, Diana’s appearance was widely viewed as her response to the controversy.

Her stylist at the time, Anna Harvey, reportedly said Diana “wanted to look a million dollars”.

Diana had initially planned to wear a less striking Valentino gown but changed her outfit at the last minute. She chose the off-the-shoulder Christina Stambolian dress, featuring an asymmetric hemline and chiffon train.

She paired it with a royal necklace, black clutch and black heels.

The dress will be displayed internationally before the auction, beginning at Sotheby’s London showroom from 18 to 24 September. It will then travel to Hong Kong, Geneva and New York.

The dress was bought at the 1997 auction by Briege Mackenzie and her late husband Graeme, who paid £39,098 for it.

Mackenzie later said they bought it for its charitable purpose rather than to wear it, as she could not fit into it. The proceeds from the original sale went towards Children First.

“My late husband and I knew that this dress was something special,” Mackenzie said in a statement released by Sotheby’s.

“Princess Diana was walking into the worst night of her life and you would never know it to look at her.”

She said the decision to sell the dress came after her husband’s death, describing their purchase of it as “one of the great days of our life together”.

A rare copy of the 1997 auction catalogue, signed by Diana and Stambolian, will also be sold alongside the dress. The catalogue credits Prince William with suggesting that Diana auction the dress.

Part of the proceeds from the upcoming sale will be donated to the Royal Edinburgh Hospital through the NHS Lothian Charity.

Another item associated with the same night, Diana’s vintage Jaguar XJ40, was sold earlier this year for £66,250.

The “revenge dress”, however, is expected to command a much higher price.