It was a call that Carole Radziwill will never forget.
Radziwill spoke to PEOPLE in this week’s cover story about her friends John F. Kennedy Jr. and Carolyn Bessette Kennedy, and the July 16, 1999, evening that their plane disappeared on the way to Martha’s Vineyard.
The Real Housewives of New York City star – who was was married to John’s maternal cousin and best friend Anthony Radziwill – received a late-night call from John’s friend “Pinky,” who was at the Martha’s Vineyard Airport awaiting the couple’s arrival.
As previously detailed in her memoir, What Remains, Radziwill used her investigative journalism background to piece together what had happened. After a few hours of making calls, Radziwill touched base with air-traffic controllers at the New Jersey airport from which John, Carolyn and her sister – Lauren Bessette – departed, soon realizing she had to report the trio as missing to the Coast Guard around 2:30 a.m.
“Once I said that out loud to the Coast Guard and made the missing persons report, I knew that this was a real thing,” Radziwill tells PEOPLE. “That was a heartbreaking moment.”
Soon after, Radziwill spoke to John’s uncle Sen. Ted Kennedy.
“He said, ‘Let’s take it step-by-step.’ He had the same tone that I had three hours earlier,” she recalls. “I felt envious of him at that moment, because he was at the beginning, when you could still believe things would end differently.”
As a search and rescue team took over, Radziwill was dismayed to hear her dear friends being referred to in past tense through television coverage, even calling ABC News to voice her displeasure.
The request gave her a last sense of control before John’s and the Bessette sisters’ bodies were found in the Atlantic.
For more on Carolyn Bessette Kennedy, pick up the latest issue of PEOPLE, on newsstands Friday.
The loss of Radziwill’s friends was followed by the death of her husband from cancer at age 40, just three weeks after the crash.
RELATED VIDEO: ‘They Would Love Hard, and They Would Fight Hard’: The Inside Story of Carolyn Bessette Kennedy’s Passionate Marriage to JFK Jr.
Eighteen years later, Radziwill – now 53 – holds her friendship with the couple close to her heart. She still misses Bessette Kennedy “after all these years,” and fondly recalls how her close friend was often at her side when Anthony was sick in the hospital.
“Carolyn was not a fair-weather friend,” she tells PEOPLE. “Whether things were going great or things were going terribly, she would be there for you. She swooped in and made all of the hundreds of hospital stays and doctors visits bearable. And she really was there for both of us nearly every day that last year of [Anthony’s] life.”