Caroline Lee Radziwill, a renowned public relations executive, classic American style icon, former princess of sorts, and the younger sister of Jacqueline Kennedy Onassis, died in New York City on Friday, WWD reports. Radziwill was 85-years-old.

Born Caroline Lee Bouvier, Radziwill dabbled in acting and interior design before rising to prominence as an era-defining socialite and, then, in the '80s as a PR executive for Armani, which WWD called the “by far the most successful of her work endeavors.” She was also hailed as a style icon, and was named to the Best Dressed List’s Hall of Fame in 1996.

While Jackie O was married to John F. Kennedy, Radziwill was adjacent to America’s unofficial royal family. But Radziwill had achieved official royal status of her own, when she married the Polish aristocrat Prince Stanisław Albrecht Radziwill in 1959. The marriage earned Radziwill the title of “Her Serene Highness.” The couple had two children, including the late Anthony Radziwill, husband of Carole Radziwill, before ultimately divorcing in 1974. Radziwill was married once more, to the American filmmaker Herbert Ross.

Jacqueline Kennedy And Princess Radziwill

Sisters and socialites Princess Lee Radziwill and Jacqueline Kennedy, sitting in the back of a car in London, May 15th 1965. (Photo by Central Press/Getty Images)

Central Press

While Radziwill was a glamorous figure in her own right—she once accompanied the Rolling Stones alongside Truman Capote during the band’s 1972 American tour—she was inextricably linked to her sister, often to her dismay. In 2016, Vanity Fair wrote about the siblings’ “complicated sisterhood,” and described the many ways in which their lives were “deeply intertwined.”

Metropolitan Museum Costume Exhibit - December 11, 1975

Lee Radziwell and Andy Warhol during Metropolitan Museum Costume Exhibit – December 11, 1975 at Metropolitan Museum of Art in New York City, New York, United States. (Photo by Ron Galella/WireImage)

Ron Galella

In his in his 1969 book, The Bouviers, John H. Davis wrote that Jackie’s “accession to the White House promised to magnify a problem [Lee] had had to cope with for some time, the problem simply of being Jackie’s sister. Although she was abundantly gifted herself … she had often been obscured by the shadow of her sister’s prominence, and now that shadow threatened to eclipse her identity.”

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Giorgio Armani, Lee Radziwill and Martin Scorsese (Photo by Ron Galella/WireImage)

Ron Galella

Radziwill went so far as to tell a reporter that she was “sick” of stories that linked her and her sister. “It’s like we’re Siamese twins!” She said.

A cause of death has not yet been announced.

Related: Why Lee Radziwill Was One of the Best Dressed American Women of All Time