Calista Flockhart reflected on playing the sister of first lady Jackie Kennedy Onassis in the new series "Feud: Capote vs. the Swans."

The Ryan Murphy-created FX show is based on the true story of famed author Truman Capote and his falling out with Manhattan's elite after he published "La Côte Basque, 1965," an excerpt from his novel, "Answered Prayers," which exposed the darkest and most scandalous secrets of his high-society friends.

The 59-year-old actress portrays Lee Radziwill, Jackie's younger sister and a Polish princess who was a member of Capote's "Swans," a group of top-tier New York socialites he befriended in the 1960s and '70s and ultimately betrayed.

"She was a pretty amazing woman," Flockhart said of Radziwill during a recent appearance on "Good Morning America." 

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"She was a New York socialite. She was at the top of her game. She was a fashion icon. She was rich. She was a princess. She was bred to marry well and marry the right man. Marry a rich man. I think she lived in the shadow of her sister.

"And so she was a woman who was in search of her own identity for a lot of her life, which she found in various ways," the "Ally McBeal" alum added. "So, she was intelligent."

Radziwill died of natural causes in 2019 at the age of 85. She was married three times, first to publishing executive Michael Canfield; then to Polish Prince Stanislas Radziwill, with whom she had two children; and, finally, to film director Herb Ross.

She was known for her impeccable sense of style and famous friends, who included Capote and Andy Warhol. 

At the urging of Capote, she began a career as an actress in her younger years. Later on, she became a successful interior designer and also worked as a brand ambassador and public relations executive for Giorgio Armani.

Radziwill and Onassis were "it girls" of the 1960s and shared a close relationship, though they were often plagued by rumors of sibling rivalry. Radziwill sharply criticized the speculation in a 1976 interview with People magazine.

"It’s just the most ludicrous talk in the world that we’re rivals," she told the outlet. "We’re exceptionally close and always have been. We’re together very often. In fact, endlessly." 

When asked if she has lived in Onassis' shadow, Radziwill replied, "I’m nobody’s kid sister."

"It’s such a stale, rehashed question," she added. "I think it’s time to make up a new story or go to bed."

"She’s a remarkable girl," Capote said of Radziwill in the 1976 People story. "She’s all the things people give Jackie [Onassis] credit for. All the looks, style, taste — Jackie never had them at all, and yet it was Lee who lived in the shadow of this super-something person."

"Feud: Capote vs. the Swans" is the second installment of Murphy's "Feud" anthology series after 2017's "Feud: Betty and Joan," which followed the rivalry between Hollywood icons Joan Crawford and Bette Davis.

Based on Lawrence Leamer's book, "Capote's Women: A True Story of Love, Betrayal, and a Swan Song for an Era," the show stars Tom Hollander as Capote along with Naomi Watts, Demi Moore, Chloë Sevigny, Diane Lane, Molly Ringwald, Ella Beaty and the late Treat Williams.

During her "GMA" appearance, Flockhart explained why she decided to take on the project.

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"First of all, I was a huge fan of the first ‘Feud,’" she said. "It was amazing. Loved it.

"I'm a huge fan of Ryan Murphy. I'm a huge fan and friend of [executive producer and screenwriter] Jon Robin Baitz, otherwise known as Robbie.

"And then all these actresses. It was just kind of a dream. It was a lot of fun. It was a lot of hard work. It was a little intimidating at first but …"

"It ups your game," host George Stephanopoulos said.

"It ups your game," Flockhart agreed. "Gotta rise to the occasion."

At a recent press conference for the series, Flockhart told Fox News Digital it was a "joy" for her to work with "these iconic women."

"They're all so talented, and the set was really supportive. And it was really fun to go through it with everybody and to play with everybody and Tom as well," she said.

During her "GMA" appearance, Flockhart said she was also a "big fan" of Capote, noting his betrayal of the swans was "the story."

"He ingratiated himself into their lives, and he befriended them, and they opened up to him," she said. "We opened up to him and confided in him, and then he wrote about them and exposed them."

"La Côte Basque, 1965" was Capote's thinly-veiled work of fiction based on the swans and the stories and salacious gossip they shared with him over the years. Published in the November 1975 issue of Esquire magazine, the article was intended to be the first installment of Truman's follow-up to his acclaimed 1965 novel "In Cold Blood."

The excerpt's publication sent shock waves through the upper echelons of Manhattan society. Capote, who had achieved his long-held desire to be a member of that exclusive set, became an outcast overnight. 

Radziwill was one of the few swans who came to Capote's defense after the excerpt was published, but they later drifted apart, reportedly due to the author's alcoholism.

Truman never finished "Answered Prayers," and his social ostracization exacerbated his downward spiral into drug and alcohol abuse that ended with his death from liver failure in 1984.

During Flockhart's appearance on "GMA," Stephanopoulos noted that most of the series' action takes place at the high-society lunch tables of Manhattan.

"If you could pick anyone in history to have that kind of lunch with, who would it be?" he asked Flockhart.

"I think I would pick Truman Capote. I would like to have a word with him," she said, earning a laugh from the host.

"Not afraid that he's going to betray you after the lunch?" Stephanopoulos asked.

"I don't think he can anymore," Flockhart replied.

Fox News Digital's Anna Hopkins contributed to this report.