Back in the good old days before Megxit, the Sussexes and the Waleses were dubbed the ‘Fab Four’. Fresh, good-looking, in tune with the younger generation: they were the photogenic future of the monarchy.

All they have in common is the memory of their mother Princess Diana – and not even her ghost seems able to make them put their enmity to one side.

How it would pain her – as it pains every parent and no doubt King Charles too – to see her children so divided. But few can blame the Prince of Wales for being less than thrilled at the prospect of his errant sibling planning a permanent return to Britain.

Time and again since his departure six years ago, Prince Harry has attacked the future King. Who can forget his patronising dismissal of Prince William’s commitment to his royal duties, describing him in that devastating Oprah interview as ‘trapped’.

And what about the accusation of ‘unconscious bias’ in relation to an alleged discussion about the possible colour of Archie’s skin?

Harry did not name the supposed culprits; but a Dutch version of his memoir Spare (which the publishers claimed had been printed in error) pointed the finger at two senior members of the Royal Family.

Then there was that stuff about the bridesmaids’ dresses in which he accused the Princess of Wales of reducing his bride to tears, leaving her ‘sobbing on the floor’.

He even mocked his brother’s hair loss, describing it as ‘alarming’, and twisting the knife by adding that William’s ‘famous resemblance to Mummy’ had faded.

Those are just a few of the well-documented salvos aimed at his older brother by Harry. Yet William has never fought back publicly, never said a bad word about the Sussexes.

Regardless of how he may feel about it all in private, he has always taken his cue from his grandmother, the late Queen Elizabeth, and done his best to remain inscrutable.

Whether he will be able to maintain such dignity now that Harry is coming home remains to be seen. It’s one thing having the Sussexes lob their ‘truth bombs’ from afar; quite another when it’s in your own backyard, as they will inevitably be. Especially if it’s Harry’s intention to worm his way back into the royal fold and reclaim what he sees as his birthright now that all his other options seem to have dried up.

Who could blame William if he were finally to lose his composure and snap as he did during the famous ‘dog bowl’ incident, where the brothers came to blows after William accused Meghan of being ‘difficult’, ‘rude’ and ‘abrasive’.

There’s only so far you can push someone before they reach breaking point and Harry seems to have very little self-control when it comes to poking the bear.

That will need to change for this to work. Harry may hope to be welcomed back like the prodigal son; but he will need to learn to bite his tongue and keep his place.

After all, however much his father may delight in his return, William is the future King and Harry is on his turf now.

It is William, ultimately, who will determine Harry’s position within the Royal Family once the succession passes to him. Harry would do well to be mindful of this in his approach.

He’s not in California any more, surrounded by celebrity sycophants and yes-men only too eager to lap up his psychodrama.

Back home, William is the one who holds all the cards and his future power ensures that only the boldest (or most arrogant) will side with Harry.

Of course, the Sussexes will have no shortage of powerful allies and acolytes beyond immediate royal circles. If it’s true that they intend to settle in the Cotswolds, where London’s rich and fashionable go to cosplay being country folk at the weekends, standing out like sore thumbs in their suspiciously shiny Range Rovers and spotless wellies, they will have no shortage of invitations.

That wealthy showbiz Soho Farmhouse set will welcome the Sussexes with open arms and gravitate to the new arrivals like bees to honey (or wasps to Meghan’s sickly strawberry jam).

Indeed, if it’s also true that the duchess has been offered a role in the new series of Guy Ritchie’s wildly successful Netflix show The Gentlemen, they already have. Archie and Lilibet will have no shortage of new friends – indeed I’ll wager that every parent at every prep school in the area is busy dreaming up ruses for their little ones to cross paths with the royal siblings. You can just hear those elbows being sharpened.

It will be a social whirl of parties and playdates – and believe me, that set knows how to have fun.

But there are other circles – more old money, more aristocratic, fiercely aligned to the King – where the couple will not be so welcome. And they will not take kindly to any Sussex shenanigans on home turf. No one knows how to freeze someone out like the British upper classes.

Truth is, things have changed a great deal since the Sussexes left six years ago. Far from being diminished by their absence (as no doubt they had hoped), the Royal Family has grown in both strength and popularity.

Adversity seems to have brought out the best in them. While Harry and Meghan have been throwing tantrums, alliances have formed in support of one another, and new players have come to the fore.

In particular, the royal women have, each in their own way, stepped up to the plate and really established themselves as forces in their own right. Queen Camilla, the Princess of Wales, the Duchess of Edinburgh and stalwart Princess Anne: they have shown what strength there can be in quiet perseverance. They now represent a formidable quartet of soft power, one which is aligned in its unfailing loyalty to the King and the legacy of the Crown.

All are working royals, 100 per cent dedicated to public life. Between them they carry out a huge number of official engagements, rarely if ever putting a foot wrong.

They work hard, keep their heads down and operate with a mixture of dedication and discretion that is the very definition of royal duty.

At every turn in the Megxit saga, these four remarkable women have presented a united front, sharing the workload left by the Sussexes’ absence with grace and gusto, earning the respect and affection of the British public along the way.

It is who are now the Fab Four, the pillars of the House of Windsor. And if Meghan and Harry don’t keep their noses clean, they will soon discover that they can also be formidable adversaries.

Not only are these women individually liked by the British people (they all rank in the top six most popular royals, with the Princess of Wales at No2 after her husband, Princess Anne No3, and the Duchess of Edinburgh and Queen Camilla Nos 5 and 6 respectively), together they fulfil all the requirements of what it means to be a royal.

Where once Meghan seemed like a breath of fresh air, a much-needed injection of carefree glamour into a rather stuffy and old-fashioned institution, now they have no need of her.

Catherine and Sophie provide the glamour, Queen Camilla and Princess Anne the experience and wisdom. Meghan, with all her histrionics, is surplus to requirements. And unlike the Duchess of Sussex (who was never especially keen on carrying out her duties as a working royal), they are grafters, not grifters.

Princess Anne is the one who takes on the lion’s share of public engagements – almost 500 last year alone. Sophie, Duchess of Edinburgh, is second in that league table (235 last year), with Queen Camilla only slightly behind at 228, which given her age (79) is quite a remarkable tally.

The Princess of Wales, understandably given her recent illness, has been less active (68 last year) – but her appearances have a major impact. Either way, between the four of them they carried out more than 1,000 public engagements last year with not a single grumble or word of complaint.

But it’s not just their hard work that matters, it’s also their strength of character, stoicism and unwavering loyalty to the British people and the institution they serve. These are old- fashioned values that stand out in the modern world – and even more precious for it. They are also acutely aware of their privilege and mindful of their duties in respect of that privilege – again, in contrast to the entitled Sussexes.

Crucially, they are genuinely invested in the future of the monarchy: they know they are mere custodians of their respective roles and understand – as the late Queen did – that the institution will endure long after they have gone.

Unlike Harry and Meghan, who seem to believe the opposite – that the monarchy exists to serve them (and help them make money) – the new Fab Four understand, appreciate and respect the Crown.

Yes, they have their own passions and pursuits (the Princess of Wales’s photography, Princess Anne’s horse riding) – but they don’t trade on their royal status.

All four have worked very hard to earn the love and respect of the British people and they don’t take any of it for granted. Camilla especially has had to earn her stripes in the face of understandable hostility towards her for the way her affair with King Charles profoundly affected Princess Diana.

But she has worked tirelessly to redeem herself and her support for the King, especially during his illness, has been invaluable. She knows she will never win over everyone; but she has done as much as anyone in her difficult position could ever do to make things right.

The way that each of these women has faced adversity and overcome it gives them a strength that Meghan and Harry, who have always blamed everyone else for their troubles, and never seemed able to accept responsibility for their mistakes, simply lack.

If anyone can safeguard the King and Prince William from the inevitable psychodrama that will accompany the return of Harry and Meghan, it is they. I certainly would not want to find myself in Meghan’s shoes, facing all four of them across the damask in the drawing room at Balmoral.

They will be the key to any attempt by the Sussexes to re-establish themselves in royal circles. Such is their influence with royal menfolk that without their endorsement there can be no real prospect of a return to the fold.

That is not to say it cannot happen; but if the Sussexes attempt to hurt or undermine the Royal Family, or pull a fast one as they have done in the past, they will have these four queens to answer to.