Earl Spencer has insisted he is ‘telling the truth’ about a phone call with Prince Charles in the days following the death of his sister Princess Diana.

In his new autobiography – exclusively serialised in the Daily Mail – the Earl claims  Charles told him ‘we’ll forget her [Diana] soon enough’ during an argument over William and Harry’s involvement in her funeral. 

Buckingham Palace hit back with an ‘unprecedented’ strongly worded response, suggesting that grief had clouded Earl Spencer’s ‘reason, judgment and memory’. 

But the Earl has now doubled down on the account he gave in Swan Song: Diana, My Sister, saying ‘I can tell you here and now, those are exactly the words he said.’

Speaking from his Althorp estate in Northamptonshire, Earl Spencer also questioned whether the official response showed whether the King was actually embarrassed.

And when pressed on whether he had evidence to back up the allegation, he said he told family and friends at the time what had been said ‘because it was so monstrous’.

‘I’ve only ever had two calls on the line with Prince Charles at any stage of my life,’ the Earl told the BBC’s Laura Kuenssberg.

‘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.’

Earl Spencer has insisted he is ‘telling the truth’ about remarks made by the then-Prince Charles in the wake of Princess Diana’s death

Earl Spencer is seen being interviewed by Laura Kuenssberg at his Althorp estate ahead of the publication of his book

Charles and Diana are seen visiting Venice during their trip to Italy in May 1985

Alluding to the Palace’s statement, he added: ‘Genuinely, that is what he said. I don’t hear him saying he didn’t say that.’

The earl claims Charles ‘went ballistic’ and ‘ranted for a while’ after he tried to tell the future King that Diana would not have wanted William and Harry to walk in her procession.

‘And then he stopped and I thought, oh now, now he’s gonna pull himself together and say something more appropriate,’ he said.

‘And then, he said, ‘we’ll forget her soon enough’.’ 

Earl Spencer added that the remark ‘stunned’ him, and that he hung up.

The book’s first astonishing extract made headlines around the world and is splitting society, with rival camps backing either side.

In the first extract, published online yesterday and in today’s Daily Mail, the earl claims:

• The late Queen dramatically offered to restore Princess Diana’s royal title on the day of her funeral;
• Diana told her father she could not go through with the marriage to Prince Charles a month before the wedding – but he told her it was ‘impossible to pull out’;
• The day before the wedding Charles told Diana that while he was happy to marry her, he was not in love with her;
• Diana was so unhappy that she considered suicide and drove herself ‘more than once’ to Beachy Head cliffs in East Sussex;
• Charles sounded ‘giddily elated – like a lottery winner’ shortly after Diana’s death.

His explosive memoir – Swan Song: Diana, My Sister – is one of the most anticipated books of the year and is due to be released next week

Earl Spencer walks with Laura Kuenssberg in the grounds of the Althorp estate 

A portrait of Diana is on display at Althorp House where her brother Earl Spencer was interviewed by Laura Kuenssberg

A second extract was published on DailyMail.com this afternoon, in which the Earl alleges the Royals allowed a tormented Prince Harry to ‘spin out of control’ after his mother’s death. 

Speaking of the day of the funeral, he writes: ‘I could not get over how tiny, and slight, and bereft, Harry looked. 

‘Too small to be doing this, I thought, and wondered how on earth this heartbroken child could bear the ordeal of that moment, or how he could possibly be expected to deal with the agony that the day ahead would insist upon.’

The Earl also gives a heartbreaking account of how a friend drove him to Chapel Royal – a small place of worship across the road from St James’s Palace where Diana’s coffin was placed in the days before her funeral.

The passage reads: ‘I had come to sit with Diana, alone. 

‘Dappled sunlight from the high stained-glass windows played across the coffin that both formed the focus of the room and presented me with the stark evidence of Diana’s death.

‘I sat down lightly beside it and began to talk to my sister for some time, expressing love and grief, and making promises on her behalf.

‘After a short while, I remembered that I had my eulogy in my pocket, and it occurred to me that I should read it to her.’

Prince Harry stands between Earl Spencer and Prince Charles outside Westminster Abbey during the funeral procession for Princess Diana on September 6, 1997

Announcing the book last month, Earl Spencer said that, ahead of the 30th anniversary of Diana’s death next year, he wanted to write down his own thoughts and memories ‘rather than having the discomfort of again reading the opinions of others’.

Prince Harry and Prince William, aged 12 and 15, ultimately did walk behind Diana’s coffin in her funeral procession in September 1997 alongside Charles, Prince Philip and Earl Spencer.

Harry would later tell Newsweek magazine of the decision: ‘My mother had just died and I had to walk a long way behind her coffin, surrounded by thousands of people watching me while millions more did on television.

‘I don’t think any child should be asked to do that, under any circumstances. I don’t think it would happen today.’

The Duke of Sussex, newly returned to the UK with his wife Meghan and their two children, is ‘aware’ of the book but has not read it, sources have told the Mail.

He ignored questions from reporters about it last night as he attended the inaugural Invictus Spirit Awards at the historic Old Royal Naval College in Greenwich.

Swan Song: Diana, My Sister is due to be published next week.

However, several copies of the book were stolen from a lorry parked in a lay-by in the Netherlands earlier this week. 

The tomes had been wrapped in black plastic to hide their contents, but publishing insiders believe they may have been deliberately targeted in an audacious bid to steal them before the official release.

• Read part one of our exclusive serialisation of Swan Song: Diana, My Sister – the searing memoir that has started a war of words with the King – here 
• Read part two: Earl Spencer criticises the royals’ ‘lack of obvious care’ for Prince Harry on the day of his mother Diana’s funeral