A previously unseen letter from Princess Diana reveals she participated in her landmark 1995 BBC Panorama interview partly to demonstrate the value of meaningful communication to her sons, Princes William and Harry.
The handwritten correspondence, penned on Kensington Palace stationery and dated November 27, 1995, has remained in the possession of the viewer, Michael Barratt, for 30 years.
It will go under the hammer at Reeman Dansie auctioneers in Colchester, Essex on June 9, with an estimated value of £3,000 to £4,000.
In the explosive broadcast, which drew an audience of 23 million, Diana famously declared of her husband's relationship with Queen Camilla: "There were three of us in this marriage."
Princess Diana being interviewed by Martin Bashir for Panorama
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Mr Barratt was moved to write a supportive message to the princess after viewing the interview on November 20, 1995, expressing that moving forward from difficult circumstances takes time but that life can improve.
To his astonishment, Diana responded personally within a week, expressing gratitude for his kindness and stating her hope that the programme would assist women facing similar struggles.
The two-page letter, signed: "With my best wishes, Yours sincerely, Diana," also conveyed her desire for William and Harry to draw lessons from her public candour.
Auctioneer James Grinter described the correspondence as exceptional: "To his great surprise, a week later, he received this wonderful reply. This has got everything you could possibly want."
Princes William and Harry pictured in 1995 with their parents, Charles and Diana
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The same auction features a rare Madame Tussauds sittings sheet dated April 18, 1996, documenting the museum's assessment of Diana at Kensington Palace before crafting her waxwork figure.
The document contains detailed observations about the princess's appearance, noting her hair was in "very good condition" and recording her preferred cosmetics, including Lancome black eyeliner and Estee Lauder rose lipstick.
Mr Grinter highlighted the significance of the item: "This is a unique opportunity to study the styling used by one of the most famous women in the world."
The sittings sheet carries an estimate of £500 to £1,000.
Princess Diana pictured with her two sons on December 21, 1995 - the day after it was reported the Queen had urged Charles and Diana to divorce
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Princess Diana wearing her engagement ring on her first royal outing post-divorce in August 1996
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The interview with the now-disgraced journalist resurfaced in headlines more than two decades later when the 2021 Dyson Inquiry exposed how Bashir employed forgery and deception to secure access to Diana.
The investigation found Mr Bashir had presented fabricated bank statements to Earl Charles Spencer, suggesting his former security chief was being paid by tabloids and intelligence services to monitor the princess.
Mr Bashir also fed Diana false claims that then-Prince Charles was conducting an affair with royal nanny Tiggy Legge-Bourke, now Alexandra Pettifer, including invented details about a pregnancy and abortion.
Despite Diana's intentions, the broadcast resulted in Queen Elizabeth II pressing her eldest son and his wife to divorce, which was finalised in August 1996. Diana died in a Paris car crash the following year.