Carolyn Bessette Kennedy's mother warned JFK Jr not to pilot plane with daughters

The mother of Carolyn Bessette-Kennedy warned John F. Kennedy Jr. not to pilot a plane with her daughters ahead of their doomed flight, a new book claims.

In JFK Jr.: An Intimate Oral Biography, the couple's assistant and close friend, RoseMarie Terenzio, recalls the events of that evening.

Terenzio spent the evening of July 16, 1999 in the couple's Tribeca, New York apartment after her air conditioning broke.

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John was flying his Piper Saratoga that evening with wife Carolyn, 34, and her sister Lauren, 33, on board.

He was expected to drop Lauren off at Martha's Vineyard before he and Carolyn would continue onto Hyannis Port, Massachusetts for the wedding of John's cousin Rory Kennedy the following day.

Terenzio explains in the book she received a call after 10pm from the wife of Anthony Radziwill, John's cousin.

The couple became concerned after JFK Jr's plane failed to arrive at Martha's Vineyard, prompting a frantic search.

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The plane hadn't arrived in the Vineyard. No one knew where they were.

Terenzio began making phone calls to find out what she could, including to the airport in Caldwell, New Jersey, where the plan took off.

She also spoke with Carolyn and Lauren's mother, Ann Freeman.

"She was panic-stricken," Terenzio said in the book, of which an exclusive excerpt has been published in PEOPLE.

"She said something like, 'I told him never to take two of my girls up at the same time.'

"She was angry. Crying. It was panic, shock. Disbelief."

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The plane crashed into the water approximately 11km from Martha's Vineyard, killing all three on board.

The National Transportation Safety Board later determined the probable causes of the accident to be "the pilot's failure to maintain control of the plane during a descent over water at night, which was a result of spatial disorientation.

Factors contributing to the accident were named as "haze" and the dark night.

John was not trained to fly at night which would require instrument training.

His instrument training was reportedly limited and he flew using visual cues, which would have been difficult that evening.

This year marks 25 years since the tragic crash.

The new book has been written by PEOPLE editor-at-large Liz McNeil and RoseMarie Terenzio.

Carolyn and Lauren are survived Lauren's twin sister, Lisa.

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