Princess Diana hoped her Panorama interview would teach her sons, Prince William and Prince Harry, about the "importance of communication", according to an unearthed letter.
The handwritten correspondence, which is going under the hammer with Reeman Dansie auctioneers on 9 June, was addressed to Michael Barratt and written on 27 November 1995, a week after her famous interview.
The former Princess of Wales, who died aged 36 in 1997 in a car crash in Paris, opened up about her wishes for her sons William and Harry in the two-page letter on Kensington Palace-headed paper, and her hopes they would reach a "deeper" connection one day.
The late Princess's words appear particularly poignant in hindsight, given that William and Harry are sadly no longer believed to be in contact.
Contents of the new letter
"She hopes the Panorama interview will help other women in similar difficulties and she looks forward to the future and sharing with and teaching William and Harry the importance of communication on a deeper level," a description on the auctioneer's website reads.
It was signed: "With my best wishes, Yours sincerely, Diana," and stayed in Michael's possession for three decades.
© Tim Graham Photo Library via GetThe auctioneers said: "Mr Michael Barrett watched the Panorama interview on 20th November 1995 and was so moved by it he sent Princess Diana a supportive letter telling her how hard it can be to move on and that life can be better in time.
"To his great surprise, a week later, he received this wonderful reply, which he has treasured ever since."
© Getty ImagesThe rare letter is expected to reach up to £4,000 at auction in Colchester, Essex.
It comes just days after unseen photographs of the late royal were revealed by auctioneer Gorringe's, depicting her during her schooldays in the 1970s.
Diana's Panorama interview
Princess Diana's BBC Panorama interview with Martin Bashir in 1995 was watched by 23 million people.
During the 54-minute interview, she famously opened up about Prince Charles's relationship with Camilla Parker-Bowles, including the revelation that there were "three of us in this marriage".
© Corbis via Getty ImagesShe also revealed her struggles with bulimia and spoke about how lonely and isolating royal life can be.
However, it was later revealed that Martin Bashir deceived Diana's brother, Charles Spencer, to secure a meeting with Diana and manipulate her into agreeing with the interview.
Earl Spencer claimed he had been shown "false bank statements" by Martin Bashir, used to help gain access to the Princess.
In 2021, an inquiry by Lord Dyson found that the disgraced journalist had deployed "deceitful behaviour" to secure the interview, in a "serious breach" of BBC editorial rules.
In a video statement, Prince William said the corporation had "failed my mother" and called the findings "extremely concerning".
Harry said, "The ripple effect of a culture of exploitation and unethical practices ultimately took her life."
