More than 40 years ago, Diana wore an iconic sweater that became known as the "black sheep." Now that piece of clothing could be sold for $80,000 when it goes to auction at Sotheby's.

Diana, who died in 1997, wore the red sweater with white sheep – and one black sheep – in 1981. She first wore it after she got engaged to King III Charles, who was prince back then, while attending one of his polo matches. 

The sweater, from the knitwear line Warm & Wonderful, sparked conversation worldwide and helped further the fashion brand. The company, which was founded in 1979, discontinued the iconic design in 1994 but brought it back in 2020.

The designers behind the line – Sally Muir and Joanna Osborne – said in a statement that after Diana was photographed in the sweater, they experienced a "surge in sales and public awareness for our small label, for which we will be forever grateful."

Diana, who was regarded as a fashion icon, actually damaged the original sweater and Muir and Osborne were asked by Buckingham Palace if they could replace it. They knit her a new one and later received a thank-you letter from Diana's secretary, Oliver Everett. 

Diana wore the beloved sweater several times and it became one of her most recognizable clothing pieces. A replica was included in "The Crown," the Netflix series about the royals. 

The original sweater stayed in the hands of Muir and Osborne, who found it in March while they were "rummaging through the attic searching for an old pattern."

"Now, almost four decades later, this one-of-a-kind sheep sweater is ready to make its way into the hands of a fortunate collector," they said in a statement. Online bidding will begin Aug. 31, and the sweater is expected to sell for $50,000 to $80,000. 

Diana and Charles got engaged in 1981 when she was just 19. Before becoming a princess, she was a nursery school teacher. The pair had two sons, Princes William and Harry. 

While Diana was adored by the public and known as the "People's Princess," she perhaps felt like a "black sheep" in the royal family at times. There were rumors about tension with the royal family, especially when she and Charles decided to divorce in 1992. 

She died alongside her boyfriend, Dodi Fayed, in a car accident involving paparazzi in Paris. 

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• Diana Princess of Wales

Caitlin O'Kane is a digital content producer covering trending stories for CBS News and its good news brand, The Uplift.