The King has taken the unusual step of publicly responding to criticism by the brother of his ‌late first wife Diana, saying via a spokesperson that grief could affect reason, judgment ‌and memory.

It comes amid claims in a soon-to-be published book Swan Song: Diana, My Sister, that relate to the now-monarch’s ‌conduct in the days after Diana’s death in 1997.

In it, Earl Spencer claims he had a heated conversation with the King, who at one point said “we’ll forget her soon enough”.

On Wednesday (British time), Buckingham Palace released a statement saying fraternal grief could colour recollections of events “even many years after such a loss”.

Diana died at the age of 36 when the car carrying her and her lover Dodi al-Fayed crashed in Paris as it sped away from chasing paparazzi photographers on ‌motorbikes.

Her brother, Charles ‌Spencer, ⁠alleges the reported comments were made in an argument over whether Diana and the then Prince of Wales’ children, princes William and Harry – then 15 and 12 – should walk ⁠behind her coffin during her funeral. Spencer claims he told the King that Diana wouldn’t have wanted her sons to go through something so traumatic, so publicly.

Charles Spencer (centre) with members of the royal family at Diana’s funeral. Photo: Getty

According to the upcoming book, the King then called Spencer. He said he wanted his sons to participate in the funeral procession, and cited making the same walk in the procession of Lord Mountbatten 18 years earlier as an example of what he wanted his sons to follow.

Spencer said he pointed out that the King was 30 when Lord Mountbatten died. He said the King “went nuts”.

“Prince Charles continued his stream of anger, without me interrupting. Then he stopped,” the Earl writes in Swan Song.

“I assumed the pause signalled an effort to bring himself under control, but then he unleashed down the phone what I have always taken to be his pent-up contempt for Diana, and his horror that the world was so bowled over by her death.

“‘Rest assured,’ he hissed, ‘we’ll forget her soon enough!’.”

Spencer writes that he was “so stunned” by the alleged remarks that he took a few seconds before replying: “I can’t believe you just said that”.

Diana became the most photographed woman in the ​world after marrying ‌the then Prince of Wales in a glittering ceremony in 1981. However, the marriage turned sour ​and the couple eventually divorced in 1996.

Asked about the report, a Buckingham Palace spokesperson said: “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 judgement and colour memory in ways others do not recognise, even many years after such a loss.”

It is a rare public statement from the palace, which is famously known for a doctrine – adopted under the late Queen Elizabeth II – of “never complain, never explain”.

Prior to the book’s release, Spencer said: “The aim of this book is to tell the truth about Diana ​from her brother’s perspective … I want to speak on Diana’s behalf and ​do so in an ⁠openly positive way.”

Swan Song: Diana, My Sister will be published next week and is expected to be highly critical of the royal family.

It emerged on Wednesday that copies of the book had been stolen from a delivery truck in The Netherlands ahead of its release.

-with AAP