Who Was Kathleen 'Kick' Kennedy? The Untold Story of JFK's High-Spirited Little Sister

Who was Kick Kennedy?

The untold story of JFK's rebellious younger sister  often described for her high spirits rather than for her beauty or intellect  is now coming to light in a newly released biography.

Read: Rosemary Kennedy's Dad Ordered Her Lobotomy to Prevent Pregnancy

KICK KENNEDY: The Charmed Life and Tragic Death of the Favorite Kennedy Daughter details the life of a young woman who was well aware of her family's royalty but chose to shy away from the name and ultimately passed away aged just 28.

Kick was born in 1920, nearly three years after future President John F. Kennedy, and was his closest sibling. 

As a teenager in 1938, she traveled to England during their father Joseph P. Kennedy Sr.'s appointment as U.S. Ambassador to the United Kingdom. 

Barbara Leaming, author of the newly released biography, writes that Kick was "willing to laugh at herself – her mistakes, her gaucheries, and even her physical flaws – in a way that was simply unknown among English girls," People reports.

Still, she was warmly embraced into the world of British aristocracy for her "American-ness" – especially by Billy Cavendish, the heir of the Duke of Devonshire.

After returning to the U.S., despite the war and her family's objection, Kick found a way to return to London and she and Billy Cavendish soon married. He was Protestant, which was inconsistent with her family's strict Catholic background.

Read: Did Marilyn Monroe Confront Jackie Kennedy About Alleged Affair?

But just four months into their marriage, Kick was widowed. Cavendish, the quiet and reserved counterpart to her outgoing personality, had rejoined the war effort and was killed by a sniper during battle in Belgium.

Her brother, Joe Jr., was also killed in the war just a month before.

She later rediscovered love in the arms of Earl Peter Wentworth Fitzwilliam, a married Protestant man, who was known for his drinking and gambling habits.

The ill-fated lovers were en route to the French Riviera when their plane wound up in a storm and crashed in 1948. Kick Kennedy was just 28 when she passed away, another victim of the so-called 'Kennedy Curse.'

In her 28 short years, she found herself estranged from her family. Her mother, furious about her affair with her married lover, refused to bring her body back to America, and left her in the care of her British mother-in-law.

Read: Patrick Kennedy Breaks Family's Silence, Opens Up About Their Struggles with Addiction

Her father identified the body, and was the only member of the Kennedy family to visit her British grave.

Leaming told to People magazine that Joe Kennedy, devastated by his favorite daughter's death, "was this man in this crumbled navy blue suit, and he was as crumbled as the suit was."

Watch: Historic Rhode Island Mansion Used by Jackie Kennedy is Destroyed By Massive Fire