LONDON (AP) — Buckingham Palace has firmly refuted a claim made by Charles Spencer, the brother of the late Princess Diana, alleging that King Charles III said she would soon be forgotten after her death.

In his upcoming book, "Swan Song: Diana, My Sister," Charles Spencer details the harrowing aftermath of Princess Diana’s tragic death in a car crash in Paris in 1997, when she was just 36 years old. He recounts a heated argument with the then-Prince Charles, who was Diana’s estranged husband, regarding plans for their sons, Prince William and Prince Harry, to walk behind their mother’s coffin during her funeral procession.

Charles Spencer asserts that he expressed to Charles that Diana would have opposed the idea of their young sons, aged 15 and 12 at the time, enduring such a public ordeal. According to Spencer, King Charles responded with the troubling remark: “rest assured, we’ll forget her soon enough.” He has accused the king of harboring “contempt” for his ex-wife, indicating deep-seated tensions between the royal family and Diana's relatives.

Buckingham Palace issued a strong statement in response to these claims, which is considered unusually forceful by royal standards. The statement conveyed that, while the palace typically refrains from commenting on publications, His Majesty is aware that the grief stemming from loss can cloud one’s judgment and memory in ways that may not be immediately recognized, even after many years.

The strained relationship between the royal household and the Spencer family has been widely discussed and has been depicted in various media portrayals, including the film "The Queen" and the television series "The Crown." Many observers noted that the palace's initial reluctance to publicly acknowledge the widespread grief following Diana’s death led the royal family to understand the significant connection she had with the public, which contrasted starkly with their own approach.

In the wake of Diana's passing, it became evident that her empathetic nature resonated deeply with people globally, prompting a shift in how the monarchy engaged emotionally with the public. This legacy continues to influence the emotionally attuned approaches of Prince William, Prince Harry, and, more recently, King Charles III.

"Swan Song: Diana, My Sister" is set to be published next week, with the Daily Mail having released an initial series of excerpts from the book late Wednesday.