Diana, Princess Of Wales, Arriving At A Charity Gala Evening On Behalf Of Birthright At Garrard. The Princess Is Wearing A Purple Evening Dress With A Gold And Amethyst Crucifix Suspended On A Pearl Rope. (Photo by Tim Graham Photo Library via Getty Images)

Princess Diana’s large Garrard purple diamond Attallah cross is set to lead Sotheby’s 2023 Royal and Noble sale, running from Jan. 6 through Jan. 18 in London.

The Princess of Wales adorned the Fleurée cross set with square-cut amethyst accented by circular-cut diamonds attached to a long string of pearls to a Birthright charity gala in October 1987, which supports the protection of human rights during pregnancy and childbirth. The royal wore a purple and black velvet Catherine Walker evening gown with a modernized Elizabethan collar (also known as a “Ruff”) for the occasion.

Over the years, Princess Diana borrowed the amethyst and diamond cross pendant numerous times from Garrard, who was then the royal jeweler. In fact, Garrard created her sapphire and diamond engagement ring, now worn by Kate Middleton.

After Princess Diana’s death, Naim Attallah, CBE and the former group chief executive of British luxury jewelry brand Asprey & Garrard, acquired the cross, but it was never worn by anyone other than the late princess (who was also the only person to ever wear it in public). After his death, it was passed on to his daughter, Ramsay Attallah.

Diana, Princess of Wales, wearing a long purple Catherine Walker evening gown, attends a charity evening on behalf of Birthright at Garrard the Jewelers on October 27, 1987 in London, England. (Photo by Anwar Hussein/Getty Images)

Made up of diamond floral petal shapes, the necklace was manufactured by Garrard in the 1920s as a one-time private commission for a regular client. The cross-shaped pendant is set with square-cut amethysts, boasting approximately 5.25 carats in circular-cut diamonds, and is estimated to fetch 80,000 to 120,000 pounds ($96,000-$144,400 USD), according to Sotheby’s.

Diana, Princess Of Wales, Arriving At A Charity Gala Evening On Behalf Of Birthright At Garrard. The Princess Is Wearing A Purple Evening Dress With A Gold And Amethyst Crucifix Suspended On A Pearl Rope. (Photo by Tim Graham Photo Library via Getty Images)

“Jewelry owned of worn by the late Princess Diana very rarely comes on to the market, especially a piece such as the Attallah cross, which is so colorful, bold and distinctive,” said Kristian Spofforth, Head of Jewelry at Sotheby’s London. “To some extent, this unusual pendant is symbolic of the Princess’s growing self-assurance in her sartorial and jewelry choices, at that particular moment in her life.”

The annual Sotheby’s Royal and Noble sale will include decorative items including historic jewelry, ceramics, and furniture.

Learn more about the cross pendant and register to bid at sothebys.com.