Princess Diana's 'Black Sheep' Sweater Spoke Volumes — and She Was Only 21!

Princess Diana often used her fashion choices to send a message — but few were as clear as her black sheep sweater.

Diana joined husband Prince Charles and sister-in-law Sarah Ferguson at a June 1983 polo match sporting a pullover red sweater by Muir and Osborne. It featured rows of white sheep, with the exception of one sheep in black. (The royal, who tragically died in a 1997 car crash, previously wore the top at another polo match in 1980.)

Even at 21 years old — and less than two years after her wedding — it was clear that Princess Diana felt like an outsider of the royal family.

"I don't think many people would want me to be queen, and when I say many people, I mean the establishment that I'm married into," Diana said in her famous BBC interview in 1995. "They've decided that I'm a nonstarter, because I do things different, because I don't go by a rule book, because I lead from the heart and not the head. And albeit that's gotten me into trouble in my work, but someone's gotta go out there and love people."

RELATED: The Real Story of Princess Diana's 'Revenge' Dress — and How She Nearly Didn't Wear It

Princess Diana Archive/Getty Princess Diana

Jayne Fincher/Princess Diana Archive/Getty Prince Charles, Sarah Ferguson and Princess Diana

Tim Graham Photo Library via Getty Princess Diana in 1980

Since Diana never visited their London shop, Warm and Wonderful, designers Sally Muir and Joanna Osborne believe the sweater was a gift to the royal.

"We always knit things we would like to wear ourselves," Osborne told PEOPLE about the best-selling item in 1983.

Georges De Keerle/Getty Sarah Ferguson and Princess Diana

Muir added, “The sheep jumper just seemed ironic, to have a sheep motif on a wool sweater."

They both insisted they did not design with royalty in mind and that "by coincidence our style appeals to the sort of girl that Diana is. She has a wonderful sense of fashion, and our sweater is perfect for her casual style."

Princess Diana Archive/Getty Princess Diana

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Princess Diana sent a different message in 1994 when she stepped out to a gala the night that Prince Charles admitted to being unfaithful to her in a national TV broadcast. She wore a black off-the-shoulder dress with an asymmetrical hemline and chiffon train that quickly was dubbed the "Revenge Dress."

"Of course Diana knew that all eyes were going to be on her," PEOPLE Senior Style Editor Brittany Talarico explained in the "Diana Diaries." "She didn't have to say anything with words. It was a fashion response — that dress became her clear message to Charles and the world."

Jayne Fincher/Getty Images Princess Diana

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Three years later, the dress sold for $65,000 at auction, with the money benefitting cancer and AIDS-related charities.