The American socialite Lee Radziwill, who was Jackie Kennedy’s younger sister, has died. She was 85.

The website WWD first reported the news, saying Radziwill died at home in New York City on Friday. Other outlets confirmed the news via family friends. The cause of death was not immediately known.

Radziwill was born Caroline Lee Bouvier in Southampton, New York in 1933, four years after her sister. Briefly and unsuccessfully an actor, she worked for editor Diana Vreeland at Harper’s Bazaar magazine and achieved success as an interior designer and public relations executive in the fashion industry, working for Giorgio Armani.

In a glamorous life she counted Truman Capote and Andy Warhol among her friends and she was married three times: to Michael Canfield, a publishing executive; to the Polish prince Stanislaw Radziwill; and to the choreographer and director Herbert Ross. The first marriage was annulled and the second and third ended in divorce.

Among her lovers was the British politician Roy Jenkins, a Labour home secretary and chancellor and author of a number of well-received historical and political books. She also had a relationship with Greek shipping magnate Aristotle Onassis before he married her sister. Radziwill described Onassis as “dynamic, irrational, cruel, I suppose, but fascinating”.

Jacqueline Lee Bouvier married future president John F Kennedy in 1953 and Onassis in 1968. She died in 1994.

Radziwill came to resent media attention based on her famous sibling, telling Vanity Fair in 2016: “Please tell me this is not a story about my sister and me. I’m just sick of that! It’s like we’re Siamese twins!” Vanity Fair duly told Radziwill’s story as it intertwined with that of Kennedy Onassis.

Radziwill nonetheless frequently discussed her time in and around the Kennedy White House, telling the New York Times she could not “deny those few years were glamorous. Being on the presidential yacht for the America’s Cup races, the parties with the White House en fête. It was so ravishing.”

In a 2001 interview with ABC, she told of being in the private quarters of the White House with Kennedy and her sister at the peak of the Cuban missile crisis, in 1962. She said one night the president took a phone call and then told them: “In three minutes we’ll know if we’re in all-out war or not.”

Jacqueline Kennedy, right, perches on camel with her sister, Lee Radziwill, in Karachi in March 1962. Photograph: AP

Radziwill’s friendship with Capote was both glamorous and stormy – she became one of his “swans”, the name the writer gave to his gossipy circle of socialite female friends. Capote fell out of favor with them in 1975 when Esquire magazine published La Côte Basque 1965, his thinly veiled tale of sex and dirty secrets.

Radziwill’s relationship with Capote became more bitter in the late 1970s when she sided with the author Gore Vidal in a feud. Vidal sued Capote for telling an interviewer Vidal had been thrown out of a 1961 White House party for drunken behavior. Capote claimed he heard the story from Radziwill but she responded that she had never said such a thing.

Capote called Radziwill a “treacherous lady” and began to publicly discuss the particulars of her love life, although in the past he had encouraged her to pursue an acting career and wrote the screenplay for the 1968 TV adaptation of Laura in which Radziwill starred. She also had a run in a Chicago stage production of The Philadelphia Story, but was panned.

In 1974, the CBS television network gave her an interview show, Conversations With Lee Radziwill, in which she talked with famous friends such as the ballet dancer Rudolf Nureyev. It was canceled after six episodes.

Radziwill had two children with her second husband. Her son, Anthony Radziwill, died in 1999, shortly after her nephew, John Kennedy Jr. She is survived by her daughter, Christina.