During her lifetime, Princess Diana‘s dedication to doing good and making the monarchy accessible earned her the nickname “The People’s Princess,” but there was one thing in her legacy that she regretted near the end of her life.

Just 10 days before her untimely death, Diana, who died tragically in a car accident in Paris on August 31, 1997, confided in one of her closest friends that she was harboring one big regret related to her two sons, Prince William and Prince Harry.

During a vacation in Greece in August 1997, Diana confided in her good friend Rosa Monckton, admitting that she regretted participating in her still-controversial Panorama interview in 1995—specifically because of the impact she feared it had had on her sons.

“She told me she regretted doing it because of the harm she thought it had done to her boys,” Monckton told People of the late royal’s confession, in a moment of candor that the outlet described as a “rare and deeply personal reflection on the Nov. 20 broadcast that reached an estimated 200 million viewers worldwide.”

As People notes, however, Diana’s concern wasn’t in what the 200 million viewers of the now-infamous interview might have thought of her, but on the harm she feared it may have caused William and Harry, who were 15 and 12 at the time.

William, in particular, was known to have been hurt by the interview, which left him “weeping,” according to royal author Robert Lacey.

“Before the 58 minutes ended, William was weeping,” Lacey wrote in his book, Battle Of Brothers: William, Harry And The Inside Story Of A Family In Tumult, adding that William’s housemaster at Eton, Dr. Andrew Gailey, actually found the young prince in the midst of a mini-breakdown after he watched the show. “Gailey told Diana that he found her son slumped on the sofa, his eyes red with tears.”

In her Panorama interview, Diana was incredibly candid about the struggles she had faced during her time in the royal family, opening up about then-Prince Charles‘ infidelity and the impact that his affair (with his now-wife Queen Camilla) had on their marriage, as well as her personal struggles with bulimia and adjusting to life in the royal family in general.

In the years since it aired, the controversy surrounding Diana’s Panorama interview has only grown, particularly as revelations about the deceptive tactics journalist Martin Bashir used to secure the interview—and the extend of the BBC’s knowledge of those tactics—have come to light.

“She was frail and that made her susceptible to Bashir,” Monckton explained, adding that Diana “kept it all in,” which only exacerbated things. “He’d told her she couldn’t talk about it. She cut people out because of that.”