The fury caused by Charles Spencer’s explosive memoir of his sister Diana is quite understandable. Hasn’t the King got enough on his plate, what with the scandal of his brother Andrew, the return of Meghan and Harry to Britain, the frailty of his own health?

Even if Charles Spencer is understandably still angry with his ex-brother-in-law, could he not have been kind enough to keep his thoughts to himself?

Thirty years ago, Charles Windsor was one of the most hated men in England, and his then girlfriend Camilla Parker Bowles was one of the most hated women. But time has passed.

Much to many people’s surprise, Prince Charles, who had inflicted such damage on the monarchy by his marital disaster, turned out to be a kindly, good-humoured old king, brave and dignified in his illness, and much-loved in many circles.

Mrs Parker Bowles has visibly been a wise, long-suffering companion to him. We have all committed sins in our youth. Isn’t it time to let bygones be bygones? And why should Lord Spencer selfishly come and spoil it all by writing his ‘malicious’ memoirs?

This is the line being peddled by the so-called ‘friends of the King’, who have been briefing so vigorously against Charles Spencer, hurling every possible insult against him, deriding him for his own failed marriages, and even suggesting his motives for writing Swan Song were a twisted mixture of malice and the need to pay the alimony to his third ex.

All these reactions are understandable, but they also mysteriously miss the point. It seems to me blindingly obvious that Charles Spencer was right to publish his book, and right to do so now.

First, because what he has said and written is true. The King has expostulated, but he has not denied the substantial truth of Spencer’s recollections. I am 100 per cent certain that Spencer’s recollections are true.

It is quite unthinkable that he has invented, for example, the by-now notorious telephone call which concluded with the then Prince of Wales saying: ‘We’ll forget her soon enough.’

Equally true – Charles Spencer himself told me this anecdote years ago, not that long after his father’s death – is his memory of Prince Charles, on the day of John Spencer’s funeral, saying to the young, grief-stricken earl: ‘You’re so lucky!’ Although the prince was attending the funeral of his father-in-law, the day was seen, entirely, through Charles Windsor’s own eyes. It was all about him – yet another reason for everyone to feel sorry for Prince Charles. As far as he saw things, Spencer was ‘lucky’ to inherit his father’s title, whereas poor old Prince Charles was still waiting, and waiting, and waiting, for his mother to die.

It is not entirely clear how much our King has a sense of humour. (His love of the appalling Goon Show might suggest not.) He would not have had the lightness of touch of his forebear, Prince Bertie (later Edward VII). Coming down the steps of St Paul’s Cathedral, having celebrated the Diamond Jubilee of his mother Queen Victoria, Bertie heard his equerry say what a beautiful service it had been. ‘Ah!’ said Bertie. ‘You have just spent an hour offering thanks to the Eternal Father. But I am cursed with the Eternal Mother.’

Charles Windsor has been longing all his life to be centre stage. He could not wait to be King, but his mother made him wait until she was 96. His parents neglected him, and then, after 15 years of adulthood and a series of unsuitable partners, he was married off, against his will in what was essentially an arranged marriage, to his 20-year-old bride, Diana Spencer.

Diana immediately wowed the crowds on a prodigious scale. Having played second fiddle to his mother for 30 years, Prince Charles visibly sulked and pouted while the world fell in love with his wife.

And, with appalling cruelty and clumsiness, he told her that he did not love her on the night before their wedding and continued to go on seeing Mrs Parker Bowles – the only sensible person in his life apart from his sister, Anne.

No wonder Diana was shattered by her husband’s adultery, and no wonder her brother continues to feel her pain.

I would say Charles Spencer and I were friendly acquaintances, rather than friends, but we have met on a number of occasions. I have stayed at Althorp three times and, for a while, we shared an agent.

I first met him in a modest but stylish Oxford restaurant, when he was an undergraduate wearing all the ‘subfusc’ – white tie and gown – which students put on to take their final exams. And he was being given a celebratory lunch by his sister – Diana. On that occasion, as with the next time we met, years later, when she came to lunch at the Evening Standard newspaper where I worked, she bubbled with charm, humour and delicacy. She was, in person, as on the great public stage, an embodiment of charm. And you felt that if you were married to her, you would be totally obscured. You would require profound personal humility to carry it off.

Poor King Charles is prodigiously self-obsessed. His outbursts of self-protective rage (demonstrated on the very day of his accession when the fountain pen spluttered ink as he spluttered with fury) are well known among everyone who has ever known him.

He was the worst possible husband for her, and she was the worst possible choice of wife for him. He spent the honeymoon sitting on the deck of the Royal Yacht reading twaddle by Laurens van der Post while the bored Diana chatted to the crew.

So, the whole thing is a tragedy. A true tragedy, in that probably all those concerned, flawed and imperfect as they were and are – the grannies who dreamed up the marriage, the bride and groom so ill-matched, their flawed, damaged sons – set out with the hope that they would do good.

As it was, this disastrous marriage very nearly brought the monarchy to an end. And its consequences – two traumatised sons, who are still living with the consequences and making the rest of us live with those consequences, could yet finish off the monarchy itself.

So, these things do matter.

Since I first met Spencer he has gone on to be an excellent historian and a first-rate writer. As an historian, he knows that he must set the record straight.

Although it might sound strange, it is more tactful for Spencer to do so now, while the King is still alive, rather than to wait for Charles III to die. Then it would seem like dancing on his grave.

We need to be reminded of how appallingly not only Charles Windsor, but all the Royal Family, behaved towards Diana. That is why the nation turned against all of them. It was not just the Press and the paparazzi who drove her to her desperate end, it was the callousness of the Windsors. I salute Charles Spencer for his bravery in saying all this.

He is a sensitive man who would know full well what the reaction to his book would be. The ‘friends’ of the King and the stuffpots will try to impugn Spencer’s integrity by smearing his character. But the truth is the truth. And, when you think about it – now Diana is, alas, no longer with us – no one else could have told the true story except her brother.

JAN MOIR: I just can’t accept that Prince Charles practically revelled in the death of his former wife 

Something profound and elemental emerges from Charles Spencer’s book, Swan Song: Diana, My Sister.

It is not how much he mourns his sister Princess Diana, from whom he was estranged at the time of her death. It is how much he utterly despises King Charles, a hatred that has roared away, a bitter furnace in his soul, for more than 30 years.

In the extracts published by the Daily Mail, Spencer’s undimmed malice burns off the page, a heartless corrosion that is awful to behold. In his version of events, we are encouraged to believe that the then-Prince Charles practically revelled in the death of his former wife.

Indeed, he appeared to be quite pleased that 36-year-old Diana, the beloved mother of his two young sons, met her end in a convenient car crash in Paris.

‘I suspect the prince’s first reaction must have been to think more of how this event might free him to marry the woman he loved, rather than appreciating the loss of one he did not,’ writes Spencer.

He recalls that, unlike others who telephoned to give their condolences in the days and hours after Diana’s death, Charles sounded ‘giddily elated – like a lottery winner’. What a terrible and damning allegation, backed up by precisely nothing, least of all the weight of history.

Yet, according to Spencer, the prince also sounded ‘strangely matter-of-fact, given the enormity of the disaster’.

How could he have been both these things at the same time?

By Earl Spencer’s account, while his own grief was profound, the brutish prince seemed to regard the death of Diana with all the detachment of a man who has just witnessed a bug being squashed on a windscreen.

Oh dear, how sad, never mind. That is the mood Charles Spencer ascribes to his former brother-in-law at this tragic moment of global import and personal bereavement in both their lives.

Spencer also writes that Charles said the following to him, delivered in true Bond-villain fashion, perhaps while stroking a cat: ‘Rest assured,’ he hissed, ‘we’ll forget her soon enough!’ Did he really? Not only does it not sound like King Charles, but it is also a remark you could surely put any number of interpretations upon. It is also a remark that could easily be misheard.

Isn’t it far more likely that Charles said ‘they’ll forget her soon enough’ – meaning the public, who were going crazy?

Isn’t it far more likely that Spencer’s own heightened emotional state meant he could have misinterpreted or misunderstood what was coming down the phone line from the royal residences as his own world fell apart?

The Palace responded to this latter allegation by saying: ‘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 judgment and colour memory in ways others do not recognise, even many years after such a loss.’ Recollections may vary, Mark II.

Some argue that the King should not have commented on Spencer’s words – yet I believe that he had to. The slur is so terrible, the smear so profound, that he simply could not let it lie unchallenged.

In writing these incendiary words, Charles Spencer meant to wound and harm, to thrust a dagger deep into the royal ribs, to cause as much damage as possible, to make a 77-year-old man, not in the best of health, look like a heartless, weak adulterer who simply did not care about the tragic death of his ex-wife.

Spencer’s judgment is thunderous and cruel for many reasons but most of all because it does not acknowledge a speck of humanity within the prince, or that at the worst moment in life, many of us do not behave at our best.

Ultimately, it all boils down to a choice that seems medieval – which Charles do you believe? Spencer or Windsor, the King or the earl, the husband or the brother, the aggrieved or the grieving. Well, I know who I think is the better man – and it is not Earl Spencer.

Is this a choice Prince Harry must also make? One wonders how he can remain on close terms with his fuming uncle while his father is being so viciously traduced and the monarchy attacked. It seems impossible that he can remain neutral, a gingery Switzerland of calm in this bloody war of attrition.

In later chapters, for example, the earl also recounts his version of the row regarding Prince William and Prince Harry walking behind Diana’s coffin at her funeral procession. Are we back here again? I am afraid so.

This is an issue Harry has bemoaned, too, as further evidence of the moral futility and chronic failings of monarchy.

Look. No doubt it was an ordeal; two young boys in their smart suits and neat hair, trying not to cry in front of the whole world. It still breaks my heart just to think about it.

Yet there is a price to pay for the trappings and advantages of being a member of the Royal Family – and here it was, being marched out in funeral lockstep across a city and a nation in mourning.

Perhaps, with hindsight, they could all look at it another way: that walking behind the coffin was a privilege, it was an honour, it was what was expected of them as heirs to a throne that stretches back more than 1,000 years.

She was their mother, this was their destiny – and in the end, what did it have to do with Charles Spencer? He was an uncle, a man whose views were welcomed – but surely those views could only be secondary to the wishes of the boys’ father?

From that day onwards, all four of these men had to learn how to live without a mother, without a sister and without a first wife.

Some of them, of course, have done so better than others. Spencer and Harry have much in common, for both of them are caught in the amber of three decades of hurt and resentment, unable to move on. Compare this to Prince William, whose burden grows heavier by the day but who never complains. And then there is Charles Spencer, a historian who wants to rewrite history.

Back in 1997, Earl Spencer welcomed his sister’s body back to Althorp in a way he did not welcome her presence in life. When she asked if she could live in the Garden House on the estate in 1992, he said no. Now, she lies in her island grave at Althorp but she does not rest in peace. Her brother has seen to that.

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