Just two days after her wedding to Prince Charles, Princess Diana wrote a heartfelt letter to Buckingham Palace footman Mark Simpson, revealing the loneliness she felt at the start of her royal life.

Dated July 31, 1981, the letter offers rare insight into Diana’s early days as a royal. “Dear Mark,” she began, “I just wanted to thank you for all your kindness + patience… It was so terribly lonely + we had so many laughs — for that I can’t thank you enough.”

She humorously asked if he liked her wedding dress and added, “I’m off to Britannia tomorrow, what with all those men around. I will have to keep a watchful eye on Evelyn!”—referring to her dresser, Evelyn Dagley.

Diana continued with a light-hearted tone, joking, “The bad news is that I haven’t eaten any cereal — sob. How am I going to cope without my bowls of cereal…[smiley face].”

This personal note is part of a collection up for auction by Julien’s Auctions, which includes other letters and memorabilia from the late Princess. Martin Nolan, executive director of the auction house, told People that Diana, just 20 at the time, had to quickly adapt from a normal life to royal expectations, learning protocols from the Queen and Queen Mother.

The letter highlights her bond with Simpson, who was close to her in age and helped ease her transition. Diana married Charles on July 29, 1981; they divorced in 1996, a year before her tragic death at age 36.