Carole Radziwill is opening up about the plane crash that killed her cousin-in-law John F. Kennedy Jr back in 1999

She says that she spoke to her best friend Carolyn Bessette before she and John Jr. took off from Essex County Airport in Fairfield, New Jersey

'I remember she said, "I love you." And, I don't know, for some reason I didn't say I love you back,' Radziwill says of her last conversation with Bessette

Radziwill was with her husband Anthony and the two were awaiting the arrival of the couple on Martha's Vineyard for the wedding of Rory Kennedy

She received a call just after midnight from one of John's friends saying that he had not arrived on the island and began to call around for more information

Radziwill eventually notified the Coast Guard, who found the plane three days later on July 19, 1999

On July 21, the bodies of John, 38, Carolyn Bessette, 33, and her sister Lauren, 34, were found on the ocean floor near Martha's Vineyard

Carole Radziwill is opening up about the death of her cousin-in-law John F. Kennedy Jr. and best friend Carolyn Bessette in a rare interview.

The author and Real Housewives of New York star will appear on the HLN docu-series 'How It Really Happened with Hill Harped' in an episode entitled 'JFK Jr.'s Tragic Final Flight' that will premiere on Friday.

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In the two-hour retrospective, set to air at 9pm, Radziwill details her final conversation with Bessette as well as how she went about trying to locate the couple when she learned their plane had never made it to Martha's Vineyard from New York City.

'I spent 15 years as a journalist and producer at ABC News, and I thought, "OK, I need to figure out this story and solve it somehow. I need to figure out where they are, because they're somewhere,"' says Radziwill in a clip exclusively obtained by DailyMail.com.

It was unfortunately a lost cause by that point, with the couple having crashed as they tried to land on the island hours prior.

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Rare interview: Carole Radziwill (above) is opening up about the plane crash that killed her cousin-in-law John F. Kennedy Jr back in 1999

Golden couple: Radziwill says she spoke to Carolyn Bessette (above in November 1997) before and and John Jr. took off from Essex County Airport in Fairfield, New Jersey

Radziwill had been incredibly close to John and Carolyn, having been married to his cousin and good friend Anthony Radziwill.

This is why she was one of the last to speak to the couple, who she planned on seeing the evening of the crash.

Radziwill was in his final days after a decade-long battle with cancer, and the trip was expected to be one of the last times the cousins would be able to see one another.

'Carolyn called me from the plane right before they were taking off. And I think it was probably a little bit after 8 o'clock,' says Radziwill of her conversation with Bessette earlier that evening.

'I don't remember anything really important from that conversation, I didn't certainly think it would be the last time I would speak to my friend.'

She then adds: 'I remember at the end she said, you know, "I love you." And, I don't know, for some reason I didn't say I love you back and that always stuck with me. And she said 'I'll call you when I land.' And then that was the last I ever heard from her or anyone.'

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The two were there with friends and other members of the Kennedy family ahead of Rory Kennedy's wedding that weekend.

With the festivities set to get underway on Saturday, Radziwill got a call the night before when John and his wife failed to make an appearance on the island.

'The phone rang at midnight, and I got just this sick feeling in my stomach, and it was John's friend Pinky, and he said, you know, 'Are they there with you? I'm at the airport and they're not here,'' recalls Radziwill.

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'And then, and then I thought, 'Oh. Oh s***.' And I just bolted out of bed.'

Radziwill explains how she then got to work trying to find the couple, who had just been married three years prior in a ceremony off the coast of Georgia attended by only 30 guests, including Carole and her husband.

Anthony was his cousin's best man.

First love: Radziwill was with her husband Anthony (above) awaiting the arrival of the couple on Martha's Vineyard for the wedding of Rory Kennedy

Bad news: Radzwill (above with John Jr. in 1997) received a call just after midnight from one of John's friends saying that he had not arrived on the island

'One call led to another to another to another, and I called the Hyannis Airport many times, because I assumed that they had made a mistake,' says Radziwill.

'And the whole time I'm calling John's friend and screaming into the phone, 'Please, you have to find somebody in John's family, to tell, tell them what's going on.''

Radziwill's calls were not getting her anywhere however, and she soon started to realize that authorities would have to be notified about the two, who had been flying with Bessette's sister Lauren.

'It was probably between 2 or 3 when I realized I had to call the Coast Guard and report John's plane missing,' reveals Radziwill.

'I said, 'My cousin's missing.' And, and then he took the name, and I think there was a little bit of a, like, a gasp on the other end of the phone.'

John had taken off from Essex County Airport in Fairfield, New Jersey, at 8:39pm on July 16, 1999 bound for the airfield in Martha's Vineyard.

The air traffic controller at the island airport alerted the regional FAA office in Connecticut just after 10pm when the plane had failed to arrive.

In the end, it was the conditions that evening which are believed to have caused the tragedy which took three lives.

Gone too soon: Radziwill eventually notified the Coast Guard, who found the plane three days later on July 19, 1999 (Carolyn and Lauren Bessette above in 1998)

Saying goodbye: Radziwill and Robert F. Kennedy Jr. scattering the ashes of John Jr. at sea on July 22, 1999 (above)

'The basic discrepancy was this: There were two different systems. There was an automatic system, which misgauged the weather, and led forecasters to say nine miles visibility,' explains Dr. Bob Arnot.

'In aviation terms, the weather forecast that JFK Jr. got was just plain wrong, and it's that forecast that accounted for his death.'

Three days later, parts of the plane were detected on the ocean floor.

On July 21, five days after the plane went missing, the three bodies were found and removed from the underwater wreckage.

The ashes of John, 38, his wife Carolyn, 33, and his sister-in-law Lauren, 34, were scattered at sea on July 22 just off of Martha's Vineyard by friends and family, including Radziwill.

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John Jr. made the decision prior to his death to have his ashes be scattered at sea rather than be buried alongside his father, mother, sister Arabella and brother Patrick at Arlington National Cemetery.

One month after the crash, Anthony died of cancer. He passed away just two weeks shy of his five-year anniversary.

Tragedy: A month after the crash, Radzwill's husband Anthony passed away after a decade-long battle with cancer (Carole and Lee Radziwill at Anthony's funeral on August 13, 1999)

Birthday girl: Carole and Lee remain close, and the two were out celebrating Lee's birthday just this past weekend (Lee above)

Radziwill remains close to her mother-in-law Lee though, and just this past weekend celebrated her birthday.

She posted a photo of Lee out to dinner, at Cipriani in New York City writing: 'Happy Birthday to the most interesting woman in NYC.'

When asked to describe her mother-in-law during a recent interview with Vanity Fair, Radziwill said; 'She has that feminine quality that's hard to put your finger on. Men just fell at her feet. There is an elegant casualness that I don't think I've seen since.'

She also said that when she first married Anthony, many asked if she was a Kennedy.

'I have to correct people when they say, 'Oh, you're married into the Kennedy family,'' she said.

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''No, I married into the Radziwill family.' It was a point of honor for me.'