This period includes the royal engagement and wedding to Prince Charles, the three-month-long honeymoon, Diana's first pregnancy and initial years of marriage, according to RR auction house in the US. The letters touch upon some of the most widely speculated aspects of Diana's life including her tumultuous marriage, her doubts and an indirect mention of Camilla, now married to Prince Charles.
She also talks about her weight and self-esteem insecurities, recurring depression, and despair over press intrusion.
"The weight is down to 9 1/2 stone - got into a size 29 jeans yesterday, instead of 32! So I am feeling much healthier but don't imagine a slender gal - 'cause there is still a lot to come off," the princess wrote in one of the letters.
The penned correspondence archive consist of 33 main pieces: 28 handwritten signed letters from Diana, encompassing 109 pages over 60 sheet; 26 are signed "Diana," one signed "D," and one signed, "me".
Diana met Carolyn at West Heath School when they were 12 -years-old.
They shared a dormitory then and became flatmates seven years later at 60 Colherne Court. Demonstrative of Diana and Carolyn's intense bond, Carolyn would be Prince Harry's godmother, and Diana godmother to her son Jack.
The online bidding begins on August 18.