A new book has revealed the extent to which John F Kennedy Jr and his wife Carolyn Bessette were fighting to save their marriage at the time of their sudden deaths.

The Kennedy Heirs, by Marilyn Monroe and Michael Jackson biographer J. Randy Taraborrelli, also claims the couple used drugs recreationally and that John was a jealous husband who threatened a friend of his wife when he thought they were too close.

John Jr and Carolyn were killed almost 20 years ago, on July 16, 1999, in a plane crash off of Martha’s Vineyard, Massachusetts, but the short, complicated marriage of the glamorous pair is still a source of intrigue.

“John and Carolyn loved each other, but their struggles were much more real than people realise,” Mr Taraborrelli told People on May 22.

The couple at a New York awards night in 1994. Photo: Getty

“They were working on their relationship at the time they died.

“They thought they had all the time in the world to figure this out.”

According to the book, when the late president’s son and magazine publisher first encountered the Calvin Klein fashion publicist in the mid-nineties, he was overwhelmed.

“You know how you hear about meeting a girl and knowing instantly she’s the one? Well, it happened to me,” the book claims Kennedy told a friend.

The couple’s hush-hush storybook wedding at the First African Baptist Church on tiny Cumberland Island, off the Carolinas’ coast, in September 1996, sold the dream of a fairytale romance but, according to the book, there were difficulties even before the ‘I dos’.

Feeling like a misfit after her first visit to the family compound in Hyannis Port, Massachusetts, Carolyn – reportedly grilled by matriarch Ethel Kennedy about gun laws – vowed not to go back.

But after John and Carolyn’s caught-on-camera Central Park bust-up in February 1996, Ethel summoned Carolyn to her home.

“Don’t let these men goad you into bad behaviour. You have to be better than that and you have to be bigger than that,” she said, according to Taraborrelli.

Said the author, “It was tough love because she wanted Carolyn to make it and she sensed her vulnerability.”

John and Carolyn avoid paparazzi in New York in 1997. Photo: Getty

Indeed, intense media scrutiny took its toll on the pre-Instagram-era ‘It’ girl, with Taraborrelli quoting an unnamed friend describing a scene at the Kennedy apartment after a stressful week in the spotlight.

“He [the friend] walked in just in time to see Carolyn doing a line of coke from the coffee table,” Taraborrelli wrote.

“It’s been a bad week,’ John told [the friend] as he sat down and did a line. “Look, I’m a Kennedy. Do you think this is the first time I’ve done drugs? Please.’”

Carolyn and John “had experiences the way people often do,” Taraborelli told People.

“I found no evidence of any addiction or problems for either of them.”

Carolyn at a 1998 gala. Photo: Getty

In early 1998, Carolyn reconnected with an old male friend who became a confidante and, according to The Kennedy Heirs, they shared a kiss.

Carolyn “pulled away and said, ‘No, what am I doing? I can’t be here right now,’ and quickly left,” Taraborrelli wrote in an excerpt published by People.

Two days later, the friend “opened the door to find John Kennedy, his face twisted in anger. John swung a punch. ‘Stay away from my goddamn wife.’”

Within months, John and Carolyn were in couples’ counselling.

When they were invited to John’s cousin Rory Kennedy’s wedding in Hyannis Port in July 1999, Carolyn only agreed to go after John promised he would never force her to go to the family compound again, according to The Kennedy Heirs.

Carolyn, in turn, said the marriage was on “probation.” Days later, with her sister Lauren Bessette, 34, beside her, she was on board the small plane piloted by John that crashed into the sea en route to the wedding.

All three were killed. Carolyn was 33, John 38.

Kennedy and Bessette family members on board a Coast Guard boat for a burial at sea service for the lost trio in July 1999 at Wood’s Hole, Massachusetts. Photo: Getty

“Together they had the most thrilling highs and the most crushing blows,” Taraborrelli said.

“Their love for each other was undeniable, but was it enough considering everything that was working against them?”