It’s not unusual for letters written by Princess Diana to find its way to auction, for as we well know, interest in the late royal remains high. The most recent correspondence to find itself under the hammer is a letter written shortly after her marriage to then then-prince, now King Charles III in 1981. The missive, penned in September of that year, was addressed to one of her school friends, Katherine Hanbury. The wedding of Prince Charles and Lady Diana Spencer. Bettmann It’s Hansbury who is now offering those items for sale, in an auction to be conducted by Gorringe’s Fine Art & Interiors. Along with the letter, which is accompanied by its original envelope, the lot includes a number of photos from their time together at school, as well as a colorful birthday card depicting a rabbit on horseback blowing a wind instrument, and a program from the Thanksgiving Mass celebrated at St Martin in the Fields Church, London, in November 1997. In one photo from the auction offering, the future princess appears near …