Newly released letters between Princess Diana and former British Vogue editor Elizabeth Tilberis reveal that the late princess once forgot her own wedding anniversary.
Swann Auction Galleries said six handwritten letters sent to Ms Tilberis between 1989 and 1992 portray the period in which Diana participated I several photoshoots for the esteemed magazine.
However, in a letter from March 5 1991, Diana gets the date of her 10-year wedding anniversary to Prince Charles wrong when discussing the media build-up to the July event.
"Alas, I fear that there aren't going to be any photographs released for my birthday in July - there is too much of a build-up towards the 30th & 10 years of marriage ... I do feel terribly that there is far too much of this lady in the media!" Diana wrote.
The royal couple’s wedding anniversary was actually July 29.
In another letter dated January 23 1992, Diana thanked the Vogue team for making her feel so relaxed during a shoot.
“I feel very relaxed being with the ladies so thank you for always thinking of me.”
Referring to the 1991 December issue front cover, shot by French photographer Patrick Demarchelier, Diana said: "Patrick ... was a dream & I hope he will be happy with the results!"
The letters are set to be auctioned by Swann Galleries' Autographs Auction in New York on March 21. They are estimated to sell for around £3,800 (AUS$6955) to £5,700 (AUS$10,430).