When you hear about brothers fighting within the royal family, it’s typically Prince William and Prince Harry’s estrangement that comes to mind. However, there’s definitely drama brewing between King Charles III and his former brother-in-law, British Earl Charles Spencer. Princess Diana’s brother reportedly calls the king a “bellowing buffoon” in a scathing memoir set for publication next week, and the palace has responded.Princess Diana’s Brother Makes Bold Claims In Upcoming BookEarl Spencer doesn’t seem to be pulling any punches regarding his feelings for King Charles III, recalling how his sister’s ex-husband reacted to her death in 1997. The memoir Swan Song: Diana, My Sister is set for release on September 22, in which Spencer said Diana “always tried to put her duty to the Queen first,” and that his family had always been loyal servants. In an excerpt printed by the Daily Mail, Spencer writes:I thought of my two grandmothers — stalwart servants and companions to this bellowing buffoon's grandmother. Also of all the generations of Spencers who had served King, Queen and Country dutifully, as ambassadors, admirals, courtiers, politicians and viceroys.Charles Spencer, the 9th British Earl, talks about how the now-king responded to the news of Princess Diana’s fatal crash in Paris. He said then-Prince Charles’ first reaction must have been to think that he was now free to marry Camilla, rather than mourning the loss of his former wife. Spencer writes:Unlike my other callers, who were stunned, barely able to articulate their condolences and offers of help, he sounded giddily elated — like a lottery winner, I remember thinking at the time.The Earl also reportedly says in Swan Song that he disagreed with the palace’s decision to have William and Harry, who were 15 and 12 at the time of their mother’s death, walk with their father behind Diana’s coffin. Spencer allegedly said that’s not what his sister would have wanted:It was a decision made out of fear that, if Prince Charles walked alone, members of the public might shout abuse at him. The committee realized that if they could persuade William and Harry to be there too, that would surely guarantee against insults flying.When Earl Spencer brought his concerns to Charles, calling the plan “barbaric,” he says in the memoir that Charles “hissed” of Diana:Rest assured… we’ll forget her soon enough!Several other claims about King Charles III and his relationship with Princess Diana have already leaked ahead of the release of Swan Song: Diana, My Sister, and the palace has issued a rare statement in response.What King Charles III Said About The Claims In Earl Spencer’s MemoirWhile the royal family rarely releases statements regarding books or other claims made against the palace, King Charles III has responded to Earl Spencer’s upcoming memoir, effectively denying his former brother-in-law’s recollection of events. The statement reads, per Page Six:While we do not comment on books as a matter of principle, His Majesty is mindful that the pain of fraternal grief can cloud reason, affect judgment and color memory in ways others do not recognize, even many years after such a loss.There’s undoubtedly still a lot of pain over what happened to Princess Diana in 1997. People will be able to read Earl Charles Spencer’s take on it all on Tuesday, September 22, when Swan Song: Diana, My Sister is released.