Princess Diana said some surprising things about newlywed life with the future King Charles in a letter to a friend that’s soon hitting the auction block.

On May 8, Gorringe’s auction house announced the upcoming sale of a trove of rare materials related to the late Princess of Wales, who died following a 1997 car accident in Paris at age 36.

The collection comes from Katherine Hanbury, a childhood friend of Princess Diana’s who attended West Heath Girls’ School with her between 1973 and 1977.

The lot up for auction on July 7 includes “The Honeymoon Letter,” in which the newly minted Princess of Wales shared an unexpected perspective after marrying Prince Charles, then heir to the throne, in July 1981.

“Its [sic] wonderful being married – I think its [sic] safe to say that after two months…!” she continued.

The letter also suggested that the 20-year-old newlywed was adapting to her new life within the royal fold, as she wrote, “Its [sic] a case of playing with grown-ups!”

A press release from Gorringe’s said the three-page letter was dated Sept. 27, 1981, and that Diana wrote it during her honeymoon at Balmoral in Scotland.

After marrying at St. Paul’s Cathedral on July 29, 1981, in the “wedding of the century” viewed by an estimated 750 million on television, Prince Charles and Princess Diana kicked off their three-month honeymoon with a 12-day cruise aboard the Royal Yacht Britannia.

The newlyweds traveled to Egypt and the Greek Isles before retiring to Balmoral Castle, the royal family’s private getaway in the Scottish Highlands, and the letter that Diana wrote to Hanbury there is one of several materials being auctioned this summer.

In addition to “The Honeymoon Letter,” the upcoming lot includes four color photos from Diana’s time at West Heath Girls’ School (including a group picture of her with fellow pupil Tilda Swinton, The Telegraph reported) and a program from an intimate thanksgiving service held at St. Martin-in-the-Fields in November 1997 following her death that August.

The whole collection is estimated to fetch between around $5,400 and $8,000 and will appear for sale in Gorringe’s Fine Art & Interiors sale on July 7, a few weeks ahead of what would have been Charles and Diana’s 45th wedding anniversary.

The couple welcomed sons Prince William and Prince Harry after marrying and before separating in 1992. They divorced in 1996 following allegations of infidelity on both sides and Diana died after a car accident in Paris the following year, forever remembered as the “People’s Princess” for the special touch she brought to her royal role.

Speaking about the significance of the lot going up for auction, Gorringe’s Books & Manuscripts specialist Albert Radford said, “This intimate archive offers a rare glimpse of Diana, Princess of Wales, before duty and fame had the final say. Through our client’s recollections from West Heath Girls’ School, Diana comes across as deeply unassuming and domestically minded; someone whose real ambition was simply to have a family and take pride in ordinary things.

“…She appears here as a young woman suspended between love and history – hopeful, unguarded, and not yet entirely claimed by the institution that would come to define her. In these small, fragile traces, innocence lingers – along with a quiet stubborn belief in something as simple and elusive as love.”