Diana's brother says he's 'telling truth' about king's 'monstrous' phone call - ABC News & Headlines – Australian Broadcasting Corporation

Princess Diana was killed in a 1997 car crash in Paris. (Reuters: Kimimasa Mayama)

Charles Spencer has given his first interview after a week of making explosive claims about Britain's royal family.

The accusations, which are contained in Earl Spencer's new book, have sparked a war of words with Buckingham Palace.

Princess Diana's brother defended himself in the exchange with the BBC, broadcast on Friday evening.

Princess Diana's brother has doubled down on explosive claims about Britain's royal family, insisting he is "telling the truth" and suggesting the king is "embarrassed".

Charles Spencer's numerous bombshell accusations, which are particularly critical of King Charles III, are contained in his soon-to-be-released memoir, excerpts of which have been published this week.

The most disparaging allegations Earl Spencer has made relate to phone calls he says he had with Charles around the time of Diana's 1997 death in a car crash.

Charles and Diana's acrimonious divorce had been finalised the previous year.

Earl Spencer accused the Charles of sounding "giddily elated" during a conversation on the night Diana died, and also of saying "we'll forget her soon enough" several days after the crash.

The claims have sparked a strong rebuke from Buckingham Palace. After the first excerpts were published on Wednesday, a 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 has not commented since then. Analysts have pointed out the strong choice of words used in the statement are a departure from the diplomatic language often chosen by British monarchs.

British peer Charles Spencer, a godson of Queen Elizabeth II, in 2013. (Action Images: Steven Paston)

In an interview with the BBC broadcast on Friday evening, local time, Earl Spencer defended himself.

Reacting to the palace's statement, he said: "Well, is he [the king] furious? Is he furious or is he embarrassed?"

When pressed about his claims that King Charles — who was not on the throne at the time — had told him "we will forget" about Diana, Earl Spencer said: "I've only ever had two calls on the line with Prince Charles at any stage of my life."

"I was hyper alert to what he was saying and those are precisely the words that he said and I promise that to you now."

When he was asked whether he had any evidence to back up the allegation, Earl Spencer said he had told friends and family about it at the time "because it was so monstrous".

Earl Spencer was later asked whether the public should believe him or the palace's version of events, and replied: "I'm telling the truth.

Charles and Diana were married for 15 years. (Reuters)

Britain's Daily Mail newspaper published more excerpts from the book titled Swan Song: Diana, My Sister, on Friday.

In one passage, Earl Spencer claimed Queen Elizabeth II, who was the reigning monarch at the time, had offered to reinstate Diana's HRH title hours after her funeral had concluded.

While Diana remained a princess after her divorce, the Queen symbolically stripped her of the HRH designation, in a move that had left Diana devastated.

Earl Spencer said he declined Queen Elizabeth's offer.

"The title should never have been removed during her life, in which case it would not have been necessary to offer it to her in death," he wrote in his book.

In another claim published Friday, Earl Spencer said he worried about the level of care given to Charles and Diana's youngest son, Prince Harry, on the day of the funeral.

On Thursday, Dickie Arbiter, who was Buckingham Palace's press spokesman at the time Diana died, rubbished the claims made in the book.

He told the BBC Earl Spencer was "just talking hogwash" and that King Charles had been "devastated" by his ex-wife's death.

The book is due to hit stores next week.