Ten days before her death, Princess Diana confided something quietly heartbreaking to one of her closest friends — a private admission about Prince William and Prince Harry that she never had the chance to revisit.

During a summer holiday in Greece in August 1997, Diana traveled with close friend Rosa Monckton for what would become their final vacation together. At one point, their conversation turned to Diana’s now-infamous 1995 Panorama interview — the television moment that stunned the world almost two years earlier.

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“She told me she regretted doing it because of the harm she thought it had done to her boys,” Monckton tells PEOPLE in this week’s cover story.

It was a rare and deeply personal reflection on the Nov. 20 broadcast that reached an estimated 200 million viewers worldwide. And it revealed something essential about Diana in her final days: her overriding concern remained the emotional well-being of William, then 15, and Harry, 12. Her regret was not about what she had confessed on camera, but about how it may have affected the two people she loved most.

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The 1995 Panorama interview became one of the most scrutinized broadcasts in modern history. Diana’s candor — about infidelity in her marriage, her struggles with bulimia and her life inside the monarchy — left a seismic impact on the royal family.

But in recent years, the interview’s origins have been reexamined following a 2021 inquiry led by Lord Dyson, which concluded that journalist Martin Bashir used forged documents and deception to secure access to the princess — a scheme BBC executives later tried to conceal.

Bashir persuaded her that speaking out on Panorama was the only way to reclaim her voice, feeding her fears with false claims — including that Prince Charles wanted her killed and that her son Prince William’s watch had been turned into a spying device.

Rosa Monckton and Princess Diana in 1993.Tim Graham Photo Library/Getty

“She was frail and that made her susceptible to Bashir,” Monckton says, adding that what didn’t help was Diana “kept ia all in”

“He’d told her she couldn’t talk about it. She cut people out because of that,” she adds.

Investigative journalist Andy Webb has spent nearly 20 years uncovering the full truth — first prompting media coverage and ultimately spurring the Dyson inquiry, which he says overlooked the BBC’s 25-year cover-up.

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As recently as 2024, his Freedom of Information battle forced the release of thousands of additional BBC emails, though many remain heavily redacted. Webb’s new book, Dianarama: Deception, Entrapment, Cover-Up — The Betrayal of Princess Diana, lays bare for the first time the full scope of Bashir’s manipulation.

“Her life became untethered,” Webb tells PEOPLE. “It was frenzied between the interview and her death.”

The revelations have deeply angered Diana’s sons.

Princess Diana, Prince Harry and Prince William in Sept. 1995.Anwar Hussein/WireImage

Prince William, who Webb says has a copy of his book, later said the interview fueled his mother’s “fear, paranoia and isolation,” adding: “She was failed not just by a rogue reporter but by leaders at the BBC who looked the other way rather than asking the tough questions. These failings . . . not only let my mother down and my family down; they let the public down too.”

Prince Harry was even more direct. “Our mother lost her life because of this,” he said in 2021.

Yet Diana herself never learned the full truth behind the deceit that shaped her decision to sit down with Bashir. By the time she traveled to Greece with Monckton in August 1997, she had not been told about the forged bank statements or the manipulation that had won her trust. What she did feel was the lingering weight of the interview’s impact on her sons.

The brothers have taken different paths as adults, but on this, they remain united: their mother was deceived, and her suffering was compounded by forces beyond her control.