The competition between the siblings will be laid bare in “The Fabulous Bouvier Sisters: The Tragic and Glamorous Lives of Jackie and Lee” by authors Sam Kashner and Nancy Schoenberger.

The authors explore a lifelong rift between the sisters, including Lee’s affair with JFK and Jackie marrying Aristotle Onassis, the man Lee was in love with.

According to the authors, Jackie kept an enemies list - and Lee’s name was firmly in the bad books. When Jackie died in 1994, she left nothing to her sister in her will.

In her will, Jackie reportedly wrote, “I have made no provision in this my will for my sister, Lee B. Radziwill, for whom I have great affection, because I have already done so during my lifetime”.

This cold-shoulder was a result of Lee's affair with Jackie's husband, the late John F. Kennedy. 

Gore Vidal, Jackie's close friend, revealed that Lee's first husband Michael Canfield told him that his wife had 'gone to bed' with JFK.

"There were times when... I think [Lee] went perhaps too far. Like going to bed with Jack in the room next to mine in the south of France and then... boasting about it," Canfield said.

The book delves into the “enchanted childhood” of the sisters, spent between an apartment on Park Avenue and summers in the Hamptons. However, it paints a particular picture of the life their mother was determined to carve out for her two pretty daughters.

The authors write, “Their mother remarried wealthy stockbroker and lawyer Hugh Auchincloss, setting the example for her daughters to marry well, bringing them up like geishas, to get money out of men.”

Read More: How much did Jackie know about JFK's affairs?

“The sisters loved couture and spent a fortune on their wardrobe, and had their step-father pay for their private schooling, which included studies in Europe,” the authors continued.

Ultimately, they claim that Lee, now 85, struggled with her own identity after living life in her older sister’s shadow.

For more information about the book, see the preview on Google Books here.