The conversations began shortly after Christmas, as the Queen tentatively picked up the telephone at Windsor Castle and asked to be put through to her grandson.
Some 5,500 miles away, ensconced in his new Californian mansion, the Duke of Sussex, 36, took the call he had been expecting for some time.
Deep down, both knew there was only one outcome, rendering the discussions little more than a formality.
But while Her Majesty, 94, was dealing with a pressing matter of state, tying up the loose ends of what has arguably been one of the greatest ructions of her reign, she was also keen to speak to Prince Harry on a more personal level, to check he was happy.
Before she instructed courtiers to announce that the Duke and Duchess of Sussex would not be returning to the royal fold, she needed to be sure that this was what he wanted.
She had to be certain that this new independent life he had so desperately craved was going in the right direction and that, crucially, he had no regrets.
For she knew that from this, there was no way back.
'Quasi-royal' status would never wash
The Sussexes have confounded even their fiercest critics since moving abroad.
Within months of arriving in the US, they had secured their financial futures, with multi-million pound deals to produce content for both Netflix and Spotify.
They launched their own non-profit foundation, Archewell, and the Duchess embarked on a career as a private investor.
But when they first made the dramatic revelation that they intended to walk away from their roles as working members of the Royal Family, they made clear they did not want a clean break.
They intended to maintain their royal patronages, believing they could continue to represent their various organisations by travelling back and forth from the US.
The Duke, in particular, was desperate to keep his honorary military titles, which he signalled just last month that he would fight to keep.
There was even talk at the time, when it was thought the couple would settle in Canada, that they could take on a high-profile Commonwealth role, allowing them to be “quasi” royals.
Such was the gulf between senior royals and the Sussexes on this issue that the Sandringham Summit was called – a crunch meeting in which those family members would set out their stalls, face to face.
With the Duchess of Sussex already in Canada, the Duke led these discussions on behalf of his family, outlining their desire to live an independent life whilst continuing to represent their various organisations.
But palace sources made clear at the time that this “half-in-half-out option” would be “very difficult to pull off”.
And as the Queen is likely to have gently reminded her grandson on that first call in the New Year, it was simply not possible for a member of her family to simultaneously pursue private business interests whilst also representing her on matters of state.
Tensions erupted in New Year
The issue had been quietly bubbling away under the surface for months, raised periodically during the many private Zoom calls the Queen has enjoyed as she caught up with the Sussexes and her great-grandson, Archie, who turns two in May.
It came to the fore on Remembrance Sunday, when it emerged that the Queen had refused the Duke’s request to have a wreath laid on his behalf at the Cenotaph, prompting the couple to pay their respects at a private ceremony in Los Angeles, captured by their own photographer.
But it was in the New Year that matters came to a head.
There were just three short months before the Duke and Duchess’s one-year review period was up and the Queen had no intention of letting anything slide.
Speculation had already been mounting and the monarch wanted to put it to rest.
While the Queen led the formal discussions about the Sussexes’ future, the Prince of Wales and the Duke of Cambridge were also involved, each speaking to the others individually to ensure they were all “in lockstep”.
Certain exchanges were likely to have been tense. While Prince William and Prince Harry have been building bridges, their relationship is not what it was.
Just weeks earlier, in December, the latter had illustrated how important his military links were to him in documents lodged with the High Court as part of a legal action against the Mail on Sunday.
The Duke, a former Apache helicopter pilot, argued that his reputation was “substantially” dependent on them, revealing that he was “particularly frustrated and saddened” by the false claim he had failed to maintain contact with the Royal Marines as it was his “sincere ambition” to continue to help current and former military personnel.
But ultimately, when it came to negotiations with his grandmother, the Duke knew he was fighting a losing battle.
One source close to him appeared to acknowledge the Queen’s decision early last week when they said: “The royal appointments and patronages were never in their gift.
“All they have done is express their commitment to them. There is no question that if it was up to them, they would keep them.”
You must choose, Queen told them
The Queen will have expressed sympathy for her grandson as she dealt this final blow.
Aware that his time in the Army was the making of him, she has witnessed him take that experience and use it to phenomenal effect, not least with the hugely successful Invictus Games.
But as a palace source said on Friday: “The Queen made the position clear last January and nothing has changed.
“She told them, if you want to lead an independent life, then good luck to you but you can’t do both. She has never wavered on that.
“At the same time, the Sussexes remain much-loved members of her family. They might live in the US but they are not exiled in the US.”
In order to draw a line in the sand, the Queen then wrote to the Duke and Duchess to confirm her decision.
“It will have simply said that after all the conversations, it’s clear you want to continue your independent lives and in that, we wish you the best,” a source surmised.
However, unbeknownst to the royals, as these discussions took place, the Duke and Duchess were also in negotiations of a very different kind.
It was announced just last week that they had agreed to give an “intimate” and “wide ranging” interview to Oprah Winfrey, to be broadcast on US network CBS on March 7.
It is understood that the Sussexes had hoped to let the dust settle on the announcement about their royal patronages before revealing they had recorded the interview.
But the news was leaked, prompting a rushed announcement that came barely 24 hours after they revealed they were expecting their second child.
A friend was forced to insist that the interview had no bearing on the decision to strip them of their patronages. It was not a form of revenge but had been long planned, they said.
But the couple had set down their marker. It was clear that they had no intention of resuming any form of royal role and so it was only a matter of time before Buckingham Palace made its own announcement, which came on Friday.
“The Duke and Duchess of Sussex have confirmed to Her Majesty The Queen that they will not be returning as working members of the Royal Family,” it said.
“Following conversations with the Duke, the Queen has written confirming that in stepping away from the work of the Royal Family it is not possible to continue with the responsibilities and duties that come with a life of public service. The honorary military appointments and royal patronages held by the Duke and Duchess will therefore be returned to Her Majesty, before being redistributed among working members of the Royal Family.
“While all are saddened by their decision, the Duke and Duchess remain much-loved members of the family.”
Two minutes later came the Sussexes’ own statement focusing on their own definition of duty.
“As evidenced by their work over the past year, the Duke and Duchess of Sussex remain committed to their duty and service to the UK and around the world, and have offered their continued support to the organisations they have represented regardless of official role,” their spokesperson said.
“We can all live a life of service. Service is universal.”
The carefully chosen words perhaps hinted at the tensions felt by the couple, who are known to be disappointed and upset by the decision.
“No one is doubting that they are committed to public causes,” one palace source said. “Some might argue that there is a difference between public service and philanthropy.”