An iconic red sweater worn by Princess Diana shortly after her engagement to then-Prince Charles, featuring rows of fluffy little sheep, sold at auction for $1.1 million following a frenetic bout of final bidding, Sotheby's announced Thursday.

The 19-year-old sported the knit garment -- which includes one black sheep amid dozens of otherwise white wooly creatures -- at a June 1981 polo match during her whirlwind days as a shy royal-in-the-making.

The playfully patterned "Black Sheep" sweater became one of the most emblematic articles of clothing worn by Diana, which in hindsight seems to foretell her troubled journey as a member of the British royal family.

The garment nabbed $1.1 million -- which includes fees and commission -- after a fierce battle by internet bidders.

The total was over ten times more than Sotheby's initial estimate of between $50,000 to $80,000.

Due to an avalanche of bids, the auction house extended the sale by several minutes, with the price leaping astronomically from $190,000 to $1.1 million in the final 15 minutes.

According to Sotheby's, it is the highest price ever paid at auction for a garment belonging to Princess Diana -- eclipsing her Infanta-style ball gown sold in January for $604,800 -- as well as the most valuable sweater ever sold at auction.

The sweater was created by then-little-known designers Sally Muir and Joanna Osborne and their knitting company Warm and Wonderful, which was subsequently catapulted to fame.

Weeks after Diana was photographed in the top, the designers received a letter explaining that one of the sweater's sleeves had suffered damage, and asking if it could be repaired or replaced.

The designers sent her a new one and had assumed the original was repaired and sent to a customer, but in March 2023 Osborne found the sweater in a small box in her attic.

In addition to the sweater, the auction included the letter requesting repair, as well as a thank you note from Diana's private secretary, Oliver Everett.

Diana was seen wearing the replacement at a June 1983 polo match.

Some 40 years later "Black Sheep" was re-released for sale in 2020 in a collaboration between the fashion brand Rowing Blazers and its original designers, Muir and Osborne.

The sweater was so iconic that it even appeared (via replica) in the fourth season of Netflix drama "The Crown," chronicling the House of Windsor's recent history.