A letter written by Princess Diana just before she turned 30 years old has emerged at an auction.

Images obtained by the Daily Mail show that Diana wrote the letter, dated June 27, 1991, to her friend Dudley Poplak to thank him for a gift.

"I do wonder what the next ten years will bring," she wrote. "The last ten, I have learnt a great deal in an interesting way!"

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"So many thanks, Dudley, for my pictures [and] my love, too," the royal wrote before signing her name.

Diana turned 30 on July 1, 1991. She separated from Prince Charles in 1992. The former couple finalized the divorce in 1996. Diana died in 1997, shortly after turning 36.

Diana Princess of Wales died in 1997 in an automobile accident. 

Diana Princess of Wales died in 1997 in an automobile accident.  (David Levenson/Getty Images)

The note was written on paper stamped with the Kensington Palace logo and was recently put up for auction by a retired autograph and manuscripts dealer, according to the Daily Mail.

Although it is unclear what exactly the "pictures" Diana referred to are, the princess admitted that she opened her gifts before her birthday, as the latter's date implies.

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"Since when have I be [sic.] able to keep a present for the right day & I'm afraid your three wonderful drawings were no exception!" she said.

"I am deeply touched to be given something that means such a lot to our family & that Raine hasn't put under auction!" added Diana, likely referencing her stepmother Raine Spencer.

Diana, Princess of Wales with her mother Frances Shand Kydd at the wedding of her brother Vicount Spencer to fashion model Victoria Lockwood at Althorpe in September 1989. Letters written by the two are being auctioned off.

Diana, Princess of Wales with her mother Frances Shand Kydd at the wedding of her brother Vicount Spencer to fashion model Victoria Lockwood at Althorpe in September 1989. Letters written by the two are being auctioned off. (Photo by Anwar Hussein/WireImage/Getty)

The outlet reported that a second note, written by Diana's mother, Frances Shand Kydd, is also being sold.

In the letter, Kydd praised her son, Diana's brother Charles Spencer, whom she said "took on the world" when he delivered his eulogy at Diana's funeral.

Diana's mother recalled speaking at a memorial mass held in Scotland, admitting she was "seared rigid."

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"... Since my children had taken on the world in the Abbey I really thought their mum should be able to do her home pitch," wrote Kydd.

The letters are going for an estimated £600, or about $763.96, and will be sold on July 30.