Prince Harry and Meghan, the Duchess of Sussex attend their final royal engagement at the annual Commonwealth Day service in London. Video / AP / BBC
Should a position ever need to be advertised, I would wager the key job requirements for being a member of the royal family (aside from a very particular genetic lineage) would include the ability to make small talk to an Olympic standard, significant waving prowess and a willingness to occasionally sacrifice your dignity in the name of the Queen and country.
Case in point when Camilla Duchess of Cornwall posed with a donkey and shetland pony in 2018, a well-meaning image that was always going to be met with giggles and snide jokes, or every time Kate Duchess of Cambridge has been forced to gamely play cricket while wearing heels and a prim skirt, carefully keeping her knees glued together.
Then there's Kate and Princes William and Harry. For a brief wonderful period of time the trio pluckily put their egos aside and went out and about in matching get-ups in the name of charity.
In 2016, the Royal Foundation launched Heads Together, rocking Boris Becker-esque 80s headbands, rumpling their perfect blow dry (her) and rapidly thinning locks (him and him).
Then in 2017 came the London marathon when they rolled up wearing black Heads Together jackets to jointly start the race.
Going through the photos from the outing, there are the usual royal engagement greatest hits – cheering crowds, the handing out of medals along with the never-to-be-repeated moment when the future Queen of England high-fived Superman.
However, there is one image of that day that is particularly striking, capturing a brief moment of intimacy that is arresting and powerful. Harry, William and Kate walk with their backs to the camera, the younger Prince with his hand gently resting on his brother's back, while he in turn has his hand tenderly on his wife's shoulders.
There are any number of cliches about the power of photography but this must be one of the most striking shots in recent royal history.
With rumours of a feud between the two royal couples, the brothers are now living in two different countries. Photo / Getty Images
Looking at it now, it poignantly captures how dramatically not only the Windsor family but the architecture of the institution have changed in only three years. Moreover, it encapsulates the exquisite loss of what was and what could have been.
For so long, Prince Harry was not only the world's most famous ginger but also the world's most famous (and seemingly amenable) third wheel. At official event after event, there he was alongside his sister and brother-in-law, an impish glint in his eye, injecting an amiable irreverence to proceedings.
What made this royal troika so powerful was the authenticity of the affection and warmth. This was not the rigid protocol of their father and his siblings, arms clamped to their sides as they starchily got on with their official duties.
Rather, William, Kate and Harry together showcased an intoxicating camaraderie and as they joked and laughed their way from the Olympics, to dinner with the Obamas, to a Harry Potter studio visit, along the way doing the nearly unthinkable, that is making royal duty seem … pleasurable.
Looking back, when it came to the pairing of the Cambridges and Harry, the sum was greater than the parts, a platonic HRH threesome that would have been the stuff of every palace courtier's wildest PR dreams.
When this photo was taken in London in 2017, Harry had been dating Suits star Meghan Markle for nearly a year and just over 12 months after it was taken, the couple would wed. This should have been the start of a new, even more deliriously successful chapter in royal history. Like the arrival of a new superhero, the addition of a charismatic, photogenic woman with an impressive humanitarian CV should only have strengthened this alliance further.
The world got a tantalising glimpse at what should have been in February 2018 when the two couples, speedily dubbed the Fab Four, appeared on stage together at the first (and sadly only) Royal Foundation forum. Like two sides of a royal coin, they brought with them a collective magnetism that must have made the Queen's heart skip a beat.
If things had unfolded differently, we should have ended seeing so many more photos along the lines of the London marathon shot, only this time including the group's newest recruit.
We should have been seeing shots of the Cambridges and the Sussexes side-by-side tackling issues like mental health and conservation (which are important to both couples) with a thrilling dynamism and energy.
But, there are a lot of "shoulds" when it comes to Harry and Meghan, the Duke and Duchess of Sussex, and their all-too-brief tenure as working members of the royal family.
Myriad reports have detailed quite how and when fault lines appeared between the two couples, but what is clear is just how much the royal family lost when the Sussexes swiftly left the (working) royal fold.
Not only did they speedily lose their two most captivating members whose passion (for each other and the causes close to their heart) had sparked a global resurgence in interest in the royal family, they lost all the possibility of what could have been.
The fact the "Fab Four" spectacularly failed to eventuate and relations between the Cambridges and the Sussexes spectacularly disintegrated while the world watched, goggle-eyed and hooked on the melodrama, must register as one of the greatest royal failures in recent history.
In the wash up, Harry has lost the chance to represent and work for the country he loves so much; Meghan has lost the opportunity to realise her full vision and impact as a working member of the royal family; William has lost his lifelong fraternal support and Kate has lost one of the people in her life who intimately understood the pressure of royal life, along with the chance to find an ally behind palace gates.
The "Fab Four" would have been a royal masterpiece for the ages; instead the world has been left with the bitter aftertaste of anger and hurt.
Instead, the shots from the Sussexes' final official outing at the Commonwealth Day service on March 9, the two couples barely acknowledging each other, offer a tragic visual bookend to the magic the world all too briefly witnessed at the Royal Foundation forum in 2018.
In recent weeks there have been reports that relations between the Wales men are thawing somewhat and that Prince Charles' former equerry Mark Dyer has been playing peacemaker.
Maybe, one day again, we will see an image like that London marathon one again, only this time there will be four people in the photo – wearing daggy matching jackets of course too.
