Carolyn Bessette-Kennedy’s Mother Warned JFK Jr. ‘Never to Take Two of My Girls Up’ in a Plane (Exclusive)

John F. Kennedy Jr. piloted the plane that crashed on July 16, 1999, killing all three people on board

<p>Tyler Mallory / Newsmakers / Liaison Agency</p> John F. Kennedy Jr. and Carolyn Bessette-Kennedy in Washington, D.C., on May 1, 1999.

Tyler Mallory / Newsmakers / Liaison Agency

John F. Kennedy Jr. and Carolyn Bessette-Kennedy in Washington, D.C., on May 1, 1999.

On the evening of July 16, 1999, RoseMarie Terenzio, John F. Kennedy Jr.’s assistant and close friend, spent the night at the Tribeca apartment he shared with his wife, Carolyn Bessette-Kennedy. Her air conditioner had broken, and the couple offered her their place so she could be comfortable that weekend while they were away.

John planned on flying to Martha’s Vineyard to drop off Carolyn’s sister, Lauren, that evening before continuing on to Hyannis Port, Mass., with Carolyn, where the couple was going to attend the wedding of John’s cousin Rory the next day.

But sometime after 10 p.m. that night, Terenzio got a call from Carole Radziwill, the wife of John’s cousin, Anthony Radziwill. The plane hadn’t arrived in the Vineyard. No one knew where they were.

<p>Simon & Schuster</p> 'JFK Jr.: An Intimate Oral Biography' by Liz McNeil and RoseMarie Terenzio.

Simon & Schuster

'JFK Jr.: An Intimate Oral Biography' by Liz McNeil and RoseMarie Terenzio.

Related: Carolyn Bessette-Kennedy and JFK Jr.: Inside Their Tempestuous Love Affair and Final Days: New Book (Exclusive)

Twenty-five years after the plane crash that killed John, 38, and his two passengers, Carolyn, 34, and Lauren, 33, a new book, JFK Jr.: An Intimate Oral Biography, by PEOPLE editor-at-large Liz McNeil and RoseMarie Terenzio excerpted exclusively in this week's issue, looks back at the tragedy that took three young lives — and the lasting heartbreak it caused.

For more on JFK Jr., pick up the latest issue of PEOPLE, on newsstands Friday, or subscribe here.

That night, after receiving the call from Carole Radziwill, Terenzio scrambled to track down what information she could. She called the airport in Caldwell, N.J., where John had departed, trying to find out where the plane could be. She also spoke with Ann Freeman, the mother of Carolyn, Lauren and Lauren's twin sister, Lisa.

Related: Inside the Final Days of JFK Jr. and Wife Carolyn: They 'Didn't Know What Was Going to Happen In Their Relationship'

“She was panic-stricken,” Terenzio says in the book. “She said something like, ‘I told him never to take two of my girls up at the same time.’ “

“She was angry,” Terenzio continues. “Crying. It was panic, shock. Disbelief.”

The plane crashed into the water about seven miles from Martha’s Vineyard.

In the weeks that followed, the National Transportation Safety Board investigated the crash. They 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 in the accident were haze and the dark night.”

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JFK Jr.: An Intimate Oral Biography by RoseMarie Terenzio and Liz McNeil comes out July 16 and is available for preorder now, wherever books are sold.

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