Lee Radziwill, the younger sister of former First lady Jackie Kennedy Onassis, has described the relief she felt after the assassination of JFK in a rare interview about her relationship with her sister.

Born Caroline Lee Bouvier in 1933, Lee, now 83, was Jackie’s junior by three years and spent much of her life in her elder sister’s shadow, despite her own accomplishments, beauty and sense of style.

Rarely wanting to talk of the relationship she had with the sister who would controversially marry her own former lover, Aristotle Onassis, the American socialite has spoken of the relief she felt to have the restrictions of being the sister of the First Lady lifted slightly after the 35th US President’s death.

“There were so many things I couldn’t do when my brother-in-law was president,” she said in a recent interview with Vanity Fair. “Finally, I'm free.”

She also revealed her difficulties in dealing with her sister in the wake of Jack’s death, telling a friend that Jackie slapped her on one occasion when grief overcame her. Flying from her London home to be with Jackie in the White House when she heard the news of JFK’s death, Lee attempted to help her sister, but later told a friend that Jackie, “can’t stop thinking about herself and never feeling anything but sorry for herself!”

Born into riches, the Bouvier sisters Jacqueline and Caroline Lee were raised in a 12-room duplex apartment at 740 Park Avenue in Manhattan, provided by their stockbroker father John Vernou Bouvier III, known as “Black Jack,” and summering on an estate in East Hampton.

Read more: Jackie Kennedy believed LBJ had her husband killed according to tapes

Despite enduring their parents tough divorce, the sisters remained close to both their mother and their father, visiting “Black Jack” in his new one-bed apartment in New York and living with their Mom and her new husband, wealthy investment banker Hugh D. Auchincloss, in northern Virginia.

In her 2000 book “Happy Times” Lee said that she knew early on in life that her father preferred Jackie, the woman who would become a celebrity as First Lady and named the “First Lady of Fashion.”

Her father “favored Jackie,” she said.

“That was very clear to me, but I didn’t resent it, because I understood he had reason to … she was not only named after him … but she actually looked almost exactly like him, which was a source of great pride to my father.”

Lee made her first trip down the aisle before her sister. Lee married publisher Michael Temple Canfield when she was 20 years old. Just two months later, Jackie and JFK were engaged, marrying in September 1953.

Lee’s first marriage was not to last. She began an affair with aristocrat Stanislas “Stas” Radziwill in London, who held the title of “prince” despite the fact he fled to England almost completely impoverished at the end of World War II. He had since made his money in a marriage with a Swiss heiress.

Nine years after her marriage to JFK, Jackie moved into the White House. She was 31 years old. Lee was forced to miss her brother-in-law’s inauguration as the premature birth of her second child Anna (she previously had a son Anthony with Stas) left both mother and child in poor health.

It was the White House move that rekindled the difficulties Lee previously had with being the younger Bouvier sister, according the John H. Davis, a Bouvier cousin. In his 1969 book “The Bouviers” he 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.”

Despite this, the sisters were still close and Lee often accompanied Jackie on her travel as First Lady.

“She had to travel a lot and liked to have me with her,” the younger sister recalled in “Happy Times”.

“Apart from mutual affection, I think our strong­est bond was a shared sense of humor.”

Being a part of the Kennedys’ world did not come without a certain amount of control over your life, however, and Lee’s very close relationship with Greek shipping magnate Aristotle Onassis was a cause of concern for Jack and Robert Kennedy who believed the man a “pirate.”

So great was their desire to put an end to the relationship that they allowed Jackie to travel on Onassis' yacht in the summer of 1963 – as she struggled to recover from the death of her son Patrick, who lived just 39 hours – so that the First Lady could convince her sister not to marry the tycoon.

Five years after the assassination of JFK, Jackie herself married Onassis but did not tell her sister about the wedding. Instead, it fell to Lee’s former lover to tell her that he was to marry her sister.

"He begged me to come to the wedding," Lee said, who put on a brave face despite her disappointment.

“I am very happy to have been at the origin of this marriage, which will, I am certain, bring my sister the happiness she deserves,” she said publicly at the time.

Radziwill has also spoken of her sister stealing her thunder for cleaning up the home of their cousin and aunt Big Edie and Little Edie Beale when it was discovered the two women were living in filth in their East Hampton mansion, Grey Gardens, and that the house was in danger of being condemned. She claims that it was not Jackie who helped the women to keep their home but that it was her own work.

Read more: Rare British Pathé film shows Kennedy’s 1963 visit to Ireland

H/T: Daily Mail