Princess Diana’s brother, Charles Spencer, is publicly addressing former brother-in-law King Charles III’s rare response to his book accusations. “Well, it’s not every day you’re gaslit by a king, but I was really upset with that because I thought it was very, not only condescending, but not straight,” Spencer, 62, told ABC News’ Maggie Rulli in a Sunday, September 20, interview on Good Morning America. “What I said is straight and true, and what did they come back with? That.” In a recent excerpt of his upcoming memoir, Swan Song: Diana, My Sister, Spencer claimed that Charles, now 77, allegedly sounded elated after Diana died in 1997…