Obviously, with all that's going on, they couldn't shake hands. Even a handshake, though still a rather formal greeting between two brothers, might have saved the day.
There's scope in a handshake for one to go for the warmer two-hand clasp, or a bit of extra vigour to convey some delight in finally being face-to-face.
If the brothers had shook hands, there would have been an opportunity for the wives to make some physical contact - a hug across the row of church seats, maybe even a kiss on the cheeks.
They didn't have to mean it, but it certainly would have looked better than what actually happened. Covid-19 cancelled any chance of that, of course, but even that couldn't account for the chilliness of the greeting between two once-close brothers which marred the final moments before Megxit.
Last Monday's Commonwealth Day service in Westminster Abbey was the final major royal outing for Harry and Meghan before Megxit and their stepping down as senior royals came into effect.
Harry had been in the UK since the last week of February and was joined by Meghan - without their son, Archie - a matter of days before the final big show. It spoke volumes that this was obviously the first time they'd seen each other and it wasn't even in private, where any stiffness could be worked through discreetly. Instead, it was in public, in a formal setting, with the eyes of everyone upon them.
There had, reportedly, been a bit of a kerfuffle before the ceremony happened at all. Harry and Meghan had noticed the order of service and how, unlike last year, they were not part of the top-tier royal family party processing in to the abbey behind the Queen.
Instead, the Sussexes were to sit in their seats and wait for the Queen to arrive, followed first by Charles and Camilla, then William and Kate.
Harry was, apparently, very upset about the optics of this. As a source told a US publication during the week, Harry feels that if even one member of his family had taken the side of he and Meghan when they decided to step down, the mood around this move could have been very different.
However, after Harry became upset about not processing into the abbey with the rest of his family, apparently William and Kate sought to soothe things by deciding that they too would take their seats in advance and leave only Charles and Camilla with the Queen.
What was obvious, however, is that this decision was made about Harry and Meghan, not with them.
What was obvious, when William and Kate arrived to their seats, in the front row of seats, while Harry and Meghan sat behind, beside Prince Edward and his wife, Sophie, was that they hadn't laid eyes on the Sussexes in advance.
William went oddly about picking the order of service off his seat before he sat down, turning his back on his brother and sister-in-law, who were both beaming super-hard and issuing their hellos to his bald head rather than his face.
Meghan, fair play to her, kept the smile in place. She is, after all, an actress. Meghan has training to make her capable of masking what the others really, really could not.
William, once he actually looked at Harry and Meghan, said a stiffly smiling hello.
Kate, whose eye Harry seemed most keen to meet, did not seem to utter a word in their direction, or look their way. She had the pinched and pale face of someone who might have had a row recently, or might even have been crying. Reports last week spoke of Kate's great sadness at the rift with Harry and how she misses the closeness they once had.
Lip-readers had a field day with the encounter. Harry was reported to have said to Meghan, after the Cambridges sat down: "He literally said, 'Hello Harry', and that was it, and he didn't say anything more than that."
This may have been accurate lip-reading, but there was nothing to support that he specifically meant his brother.
As Kate turned back to talk to Sophie Wessex in the seat behind her, Prince Edward leaned over to Meghan and Harry, who lifted his scowling face from his order of service and tried to chat. Meghan squeezed his shoulder reassuringly, she kept smiling and she continued smiling as they followed the Queen out of the church later.
Harry had a face like thunder. William had the face of a disappointed dad. Kate looked simply worn out.
It was, undeniably, a sad end to it all. No jolly sending of the Sussexes on their way, no spirit of wishing them well, even if the move was considered unwise by all who love Prince Harry. It was bitter and it seemed like a family irredeemably broken.
Interestingly, in the course of the prank calls released this week, Harry seemed to sum up his attitude to his position in his family.
The calls, conducted over Christmas and the new year by Vovan and Lexus, allegedly Russia's answer to Ant and Dec, and purporting to be Greta Thunberg and her father, Svante, saw Harry hold forth on Donald Trump, private jets and his own status.
"I was in the military for 10 years, so I'm more normal than my family would like to believe," he said. There's defiance there, mixed rather unappealingly with a sense of being the victim and a dose of feeling misunderstood by people whom he might wish would show a bit more empathy.
As Harry and Meghan finally exited the top tier of his family, an unnamed friend told a US publication about how sad they both feel and how, ultimately, the prince is putting his wife and child first, even if that means losing his extended family. It's a hard choice to make and it leaves you invested in your spouse to an extent that can suffocate rather than save the relationship.
But if the sibling encounter told us anything last week, it's that Harry is definitely out on his own now. It's not exactly what he wanted, but it's where we're at.