AceShowbiz - A new book drops a bombshell revelation about Prince Charles and his reaction to Lady Diana's death back in 1997. Written by historian Robert Lacey, "Battle of Brothers: The Inside Story of a Family in Tumult" claims that the British prince made an "offensive" comment about his late wife just days after the car crash that claimed her life.

It is said that the royal made the remark to Diana's brother, Charles, 9th Earl Spencer, prior to the princess' funeral. They were allegedly involved in heated discussions about the funeral arrangements. Spencer thought that Diana's young sons, Prince William and Prince Harry, should not walk behind their mother's coffin for the procession to Westminster Abbey.

"Spencer felt quite sure that Diana would have been horrified at the idea of her sons having to endure such an ordeal," Lacey writes in the book. "He had already told Charles as much."

However, the discussion seemingly didn't go well as one of their phone calls "had ended with the earl slamming down the phone on his brother-in-law after Charles had made a particularly offensive comment about Diana." The author doesn't elaborate what it was, and neither Charles Spencer nor a spokesperson for Prince Charles has responded to the book's claims.

Lacey adds in the bombshell book, "Prince Charles had no doubt that he should walk the long route with both his sons beside him. But Uncle Charles Spencer did not agree." Spencer "was already angry on his family's behalf that his sister's funeral had been hijacked into a royal occasion, and he was particularly opposed to the idea that his young nephews should have to walk the best part of a mile behind their mother's coffin through the streets."

In the end, Prince William, who was 15 at the time, and his 12-year-old brother Prince Harry took part at the funeral which was held on September 6, 1997, just six days after Diana's death.