However, when the Earl pointed out to Charles that he had been 30 at the time of Mountbatten’s death, he said the now King “went nuts”.
The Earl writes in Swan Song: “Prince Charles continued his stream of anger, without me interrupting. Then he stopped.
“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!’”
The Earl was “so stunned” by Charles’ alleged remarks, he wrote, that he took a few seconds before replying: “I can’t believe you just said that”.
The Earl ended up walking in the funeral procession alongside William and Harry, as well as Prince Charles and Prince Philip, behind Diana’s coffin as it was carried through London.
At the funeral itself in Westminster Abbey, the Earl delivered a defiant speech that has frequently been named one of the greatest speeches of the 20th century.
The shocking claims from the Earl are sure to continue as Swan Song is serialised by the Daily Mail newspaper ahead of its UK publication next Tuesday, September 22.
Charles has yet to respond to the Earl’s allegations.