It was black and strapless, with a sassy sequined flounce at the bodice and a gloriously full, swishy skirt.
The dress was, Lady Diana Spencer thought, so grown-up, just right for her first official engagement after the announcement she was to marry Prince Charles.
But when photographs emerged of the then 19-year-old Diana emerging from a limousine at a March 1981 charity event - all creamy shoulders and ample décolletage - there was a minor scandal over the revealing cut. According to Elizabeth Emanuel, who designed the ball gown with her husband, David, they didn't realize the furor the dress would cause, The Associated Press reports.
"She just looked fantastic. At that time, she was curvy. Not fat in any way, but she had cleavage . . . And she looked great in this dress," Emanuel said in an interview. "We in no way expected there to be such a reaction."
Along with other garments worn by Diana and designed by the Emanuels, it is to be auctioned off next Tuesday in London in a sale that includes the silk chiffon blouse chosen for the Princess of Wales' official engagement portrait by Lord Snowdon, and the calico prototype used to fit her famous ivory wedding gown.
"She was unsophisticated at that point, and when I look at the wedding dress and the black ball gown I can see a young girl's dream of the ultimate party dress or romantic dress," said auctioneer Kerry Taylor, whose eponymous firm is handling the sale. "So there's an innocence about these early pieces."