A number of letters written by Princess Diana that show how difficult she found her "desperate and ugly" divorce from Charles have been revealed.
The 32 "emotionally raw" letters and message cards were written to her friends Susie and Tarek Kassem during her public and acrimonious split from the now king.
In them she describes how she had been left "on my knees" over the divorce settlement.
She also writes about fears her phone was being bugged - a plot line which featured in the latest series of The Crown - makes veiled digs at the royal family for isolating her and thanks the Kassems inviting her to spend an otherwise lonely Christmas and Easter with them.
The Kassems say that owning the poignant documents is a responsibility they do not wish to pass on to their children or grandchildren and are selling them at auction for an estimated £90,000.
The proceeds will be donated to charities Diana supported.
One of the most telling letters revealing how down the divorce made Diana was written on April 28, 1996.
She wrote to apologise for having to cancel a trip with them to see the opera Tosca due to the strain it was having on her.
She said: "I am having a very difficult time and pressure is serious and coming from all sides. It's too difficult sometimes to keep one's head up and today I am on my knees and just longing for this divorce to go through as the possible cost is tremendous."
Her handwriting, normally open and flowing, deteriorates towards the end of the letter, apparently from where she was struggling as she wrote.
She also told how she feared her phone at Kensington Palace was 'constantly' bugged and the recordings of her private conversations were passed on to the Royal family.
On May 20, 1996 she wrote to Mrs Kassem: "As I don't have a mobile it is difficult to discuss personal issues as my lines here are constantly recorded and passed on.
"If I'd known a year ago what I'd experience going through this divorce I never would have consented. It's desperate and ugly."
In one remarkable letter she thanked the Kassems for letting her spend Christmas 1995 with them while William and Harry were with their father at Sandringham.
After Buckingham Palace publicly announced Diana would not be joining them for the festivities it was widely thought she spent it alone at Kensington Palace.
Tellingly she wrote: "I was so thrilled to be invited into a family occasion particularly as I was made to feel like one of the team."
In all, there are 32 letters and cards Diana wrote in late 1995 and throughout 1996 that are now being sold by the couple.
In many of them she gushingly thanks the couple - who she met for the first time in August 1995 during her regular visits to the Royal Brompton Hospital - for showering her with gifts and emotional support.
On December 19, 1995 - the day after the Queen advised Charles and Diana to divorce, she wrote: "I may have been described as a butterfly but I don't want to fly away from this loving family." She was referring to the Kassem family.
She repeatedly thanked them for being there for her and for 'listening to all my chat'. She wrote 'nice to be a threesome!'.
In another swipe at the Royal family she wrote: "I'm immensely touched by how protective you both are of me..... I'm not used to that!"
She went on to write that she "never had such love and support from a married team before."
She thanked them for gifts like flowers, meditation books and jasmine oil.
The Kassems, who live in London, have kept hold of the correspondence from Diana and are now selling it at Lay's Auctioneers of Penzance, Cornwall.
They are being sold in individual lots but have an overall estimate of £90,000.
Mimi Connell-Lay, of Lay's Auctioneers, said: "This is a really interesting collection of letters from Princess Diana. A lot of them are emotionally raw and frankly astonishing.
"Susie met Diana at the Royal Brompton Hospital and it is obvious that they clicked straight away, Diana says as much in one of her letters.
"They had a very strong connection and what is clear is how much Diana valued their friendship and support and advice at a time of great emotional turmoil for her.
"She wrote a lot about what was going on in her life at the time, especially her divorce, and repeatedly referred to not having the support from the Royal family.
"The collection of over 30 letters and notecards illustrate Diana's immensely warm and loving disposition in a charming and delightful manner. Some letters do touch on the enormous stress she was experiencing during periods of very public heartbreak,
"When we met the clients they remarked how accurate Elizabeth Debicki's portrayal of Diana in The Crown was of her at that time.
"Our clients are both aged in their 70s now. They have treasured these letters for over 25 years.
"They reflect the special and loving relationship they had with the most unique women that they had ever known.
"I think they feel they have a great responsibility owning these documents and they don't want to have to pass that on to their children or grandchildren.
"They will be donating some of the proceeds to some charities Susie and Diana were involved with."
The sale takes place on February 16.
