They last saw each other over a year ago and, in that time, the Dukes of Cambridge and Sussex have had to navigate some extremely choppy waters from either side of the Atlantic.
A pandemic, a painful falling out and the death of a most beloved grandfather. It would be a lot for most siblings to handle, let alone two brothers who have already experienced more public heartbreak than most people do in a lifetime.
Until now, they have been thousands of miles apart, but with Prince Harry's arrival in the UK on Sunday – his first time back in Britain since he and the Duchess of Sussex left for Canada with the then-eight-month-old Archie in January last year – thoughts are turning to the estranged brothers, forced back together so soon after such a fraught period. Will their grief unite or divide them? And who will help them through it all?
Jo Hemmings, a psychologist and relationship coach, says that when there is a rift between siblings, the first meeting after a long period apart can serve as a temperature test for each party. "Is there warmth? Ownership of wrongdoing? Admitting that you may have caused hurt even if you don't think you're to blame?
"Do you hug? Or does it feel cold, do you avoid eye contact, make small talk with no reference to the issue that initially caused the rift."
If you can, begin by acknowledging "hurt has been caused", she says. "Then there is a chance to repair a relationship by exploring this maybe further down the line."
They would never have wished for it, but many are speculating that coming together to grieve could bring the brothers the closeness they have been so sorely missing. Having something to focus on can be helpful when emotions are running high, says Hemmings, though for some, a sombre event like a funeral can also make it all too easy to simply put on a brave face out of respect for the occasion.
"It is perfectly possible for those two people to hide behind the occasion, to be polite, formal and play their dutiful role without any intention of pursuing a renewed relationship," she explains.
"Attending their grandfather's funeral will certainly give them both something to concentrate on but, on such a sad occasion, it is much easier for them to behave formally and emotionally disconnected from each other, than it would be if it was a happy occasion, like a marriage."
Their own emotional associations with funerals could be a binding force or a dividing one, she suggests, recalling the image of the boy princes walking behind the cortege of their mother, the Princess of Wales. "This may well trigger some distressing memories for both William and Harry, which may help them feel an emotional connection or it may work the other way, hiding their own private thoughts from each other."
One well-placed source suggests Zara Tindall has been acting as something of a peace broker between the two brothers since the Sussexes' controversial Oprah interview, which is believed to have widened yet further the vast wedge growing within the family. The cousins have always been close, as have the York sisters, but as Princess Eugenie knew the Duchess of Sussex before her marriage, Zara could perhaps be perceived to be the more impartial of the Windsor women.
Linda Blair, a clinical psychologist whose book Siblings serves as a guide to managing sibling rivalry, says having a neutral member of the family act as a go-between can be useful, but only "when both people involved in the rift have requested it and agree on the person".
"Otherwise it's not at all helpful. In those circumstances, yes it is because they felt that they want that buffer, that person who asks the questions or who redirects the building up of emotions. But only then, otherwise it feels like being pressured."
The more space that family member has from the situation the better, she says. "The more distance you have, the more able you are to manage emotions and push down any possible prejudices you might have."
Prince Philip's funeral will be a relatively small affair due to Covid restrictions but, nevertheless, a royal remembrance is always going to be scrutinised.
For the princes, the thought that their relationship could be under the microscope on such an emotional day must be painful. These things are inevitably harder, Blair says, for those people who "have to negotiate through waters while everybody watches".
"[It's] really difficult for any troubled relationship when it has to be in the spotlight."
With five days to go before they have to say goodbye to their grandfather, both men issued heartfelt statements about a man who has clearly been a constant and something of a hero to them both.
Their statements were different in tone, as you would expect from two men who have carved such distinct paths in recent years.
The Duke of Cambridge spoke of the luck he feels having had Prince Philip there to guide him "both through good times and the hardest days", and pledged to continue his lifelong dedication to the Queen.
The Duke of Sussex hailed him as "my Grandpa: master of the barbecue, legend of banter, and cheeky right 'til the end".
They might read somewhat differently, but the sentiment was the same, with both praising his sense of service and honour, and expressing gratitude on behalf of their young children.
William wrote he would "never take for granted the special memories my children will always have of their great-grandpa coming to collect them in his carriage". Harry said Archie and "his future great-granddaughter" would always hold a special place for him in their hearts.
"Losing a close, loved relative always reminds us of our own mortality and how precious our immediate family is," says Hemmings.
"If both Harry and William are willing to try to reconcile, have time scheduled alone to discuss their rift and think it is appropriate under the circumstances, this might be an ideal time to start the reconciliation process."
You have to wonder, then, if the dukes' shared love for their grandpa may well prove to be a uniting force.