The six handwritten letters, a single lot estimated at $5000-7500 (£3850-5780) for sale in Swann Galleries’ Autographs sale on March 21, reveal some of the princess’s thoughts in the run up to her separation from Prince Charles in 1992.
The letters are addressed to the late Liz Tilberis, former editor of the UK edition of Vogue (1988-1992) and then editor of Harper’s Bazaar in New York (1992-1999).
In one letter, dated March 1991, Princess Diana (1961-1997) reveals there would be no official photographs for her forthcoming 30th birthday that July. “There is too much of a build up towards the 30th & ten years of marriage…I do feel terribly that there is far too much of this lady in the media!,” she writes.
On her 30th birthday on 1 July 1991, the press revealed the princess had rebuffed Prince Charles’ attempts to host a party for his wife.
The letters also shine a light on the close ties Princess Diana had with fashion magazine journalists, relationships unusual for a royal figure.
Her friendship with Vogue journalists started in 1981 when, as Lady Diana Spencer and newly engaged to Prince Charles, she was introduced to editors such as Anna Wintour and Anna Harvey, and later Liz Tilberis, who would help build a royal wardrobe using UK designers.
While Tilberis (1947-1999) worked at Vogue, she advised Princess Diana on her image, introducing her to photographers such as Patrick Demarchelier, who went on to photograph the royal for a Vogue cover in 1994.
In another of the letters, Diana congratulates Tilberis on her appointment at Harper’s Bazaar in New York, a tenure that would transform the stuffy title into an arbiter of fashion cool.
The friendship lasted until the princess’s death in August 1997, with Diana supporting Tilberis through her battle with ovarian cancer.
Other lots include a selection of Christmas cards from Diana to Tilberis featuring photographs of her family, estimated at $700 (£540) to $1,000 (£770) .
Princess Diana was a prolific correspondent, whose letters and cards to friends and favoured staff come regularly to auction. It's a market that shows no sign of slowing down, 21 years after the princess' death.
Colchester-based Reeman Dansie holds two specialist royalty memorabilia sales a year.
There is a premium on letters handwritten by Princess Diana that mention princes William, Harry and/or Charles.
In 2017 Cheffins in Cambridge sold six letters from Diana to a Buckingham Palace steward, in which she writes about princes William and Harry, for £15,100 (plus premium). One letter, guided at £400-600, went for £3200.
Other auction lots
The Swann Galleries auction on March 21 in New York also features letters relating to the US Revolution and Civil War.
One of the oldest handwritten missives in the sale is dated June 1550, written by Cosimo De Medici, in which he issues orders to an army captain, estimate $1000-2000 (£700-1540).
A letter written in 1884 by Queen Victoria to Alfred, Lord Tennyson expresses her sorrows over the death of her son, Leopold, estimate $3,000-4,000 (£2300-3800).