Althorp House, England, UK: Britain's King Charles sounded “like a lottery winner” after the death of his first wife, Diana, her brother writes in his forthcoming book, with new extracts published on Thursday.

During the interview, Spencer said that then-Prince Charles sounded 'giddily elated' immediately after Diana died in 1997, possibly because he felt it meant he was free to marry again.

Charles, on Wednesday, took the unusual step of responding to criticism after the first extracts of Spencer's book were published in the Daily Mail, saying via a spokesperson that grief could impact reason, judgement, and memory.

Diana died aged 36 in a 1997 Paris car crash as photographers pursued her on motorbikes, sparking an outpouring of grief and a reckoning over whether the media bore some responsibility after it splashed details of her life across front pages for years.

Spencer also said Prince Harry and his American wife Meghan should be given official security as they are now treated by the media much in the same way as his late sister was in the years leading up to her death.

Charles and Diana separated in 1992 and divorced in 1996. That was a year after Diana told the BBC that “there were three of us in this marriage, so it was a bit crowded,” in reference to Charles' relationship with Camilla Parker Bowles, whom he married in 2005.