One of the late Princess Diana’s most treasured fashion items is going up for sale.

The Princess of Wales, who passed away in 1997, famously wore her iconic “black sheep” sweater back in 1981 and now the jumper will be showcased at a Sotheby’s auction later this year.

The auction house’s global head of fashion, Cynthia Houlton, gave some insight into the selling of the antiquated Warm & Wonderful sweater in a video published by Reuters recently.

The pullover was previously discovered in a box in the attic of creator and brand founder Joanna Osborne, alongside letters from Diana’s private secretary.

Diana sported the red, white and black sweater for the first time in public at one of King Charles’ summer polo matches, just months after they became engaged.

Once she was photographed wearing the jumper, Warm & Wonderful’s label “blew up” and they received “the ultimate kind of influencer coverage” back in the day.

Houlton explained that after Diana rocked the wardrobe staple, Buckingham Palace sent Osbourne and brand co-founder Sally Muir a memo noting that the sweater’s wrist had some damage.

The royal residence asked the company to replace or repair the wool article because Diana adored the sweater.

“It’s so interesting that, there’s been speculation of how much she loved the sweater but the letters actually prove that,” Houlton said.

She added that Warm & Wonderful sent Diana a brand new cardigan — much to her delight.

Diana was actually spotted rocking the replacement jumper in 1983, where she paired it with white trousers.

And so this past March, Osbourne was looking for patterns in her attic and found a box with the first ripped sweater the Palace sent back to them in 1981.

“In the 1980s, their brand was blowing up, they just assumed that the sweater got sent to another buyer, they thought it had gotten repaired but actually it had just been forgotten in this box for 40 years,” Houlton continued.

According to the executive, the product is estimated to fetch between $50,000 to $80,000. The auction is set to go down from Aug. 31 and will run through Sept.14.

The item, as well as the letters from Buckingham Palace, will first be on view at Sotheby’s London Galleries from July 17 until July 19. The artifacts will then head down to the company’s New York location in September.

“So this item has never come to market before, this is the very first time it will have ever come to market,” she said.

“If you’re Princess Diana, certainly you have access to lots of pieces of apparel you could choose to wear. And the fact that she wanted a replacement and then again two years later wore the exact same, replacement sweater, I think speaks really volumes from her how much this sweater meant to her,” she pointed out.

Houlton went on, “There really is. If we think of, you know, there are very few, I think, truly few fashion icons and Diana is always at the top of that list. [The item] really is the most iconic fashion piece that she’s ever chosen to wear.”