There are very few certainties in life but one thing we can say with rock-solid, absolutely unequivocal confidence is that the world has never, and will never, see the Queen in shorts.
Ditto her son, lifelong regal intern, Prince Charles. The only reason we know that he actually has knees is down to his penchant to slip into a kilt the minute he is north of the border and hits Scotland. (Well, that and the palace's failed attempts to pass him off as some sort of dashing action man figure in the 70s which saw some contrived beach shots hit the front pages.)
But the thing about a new sovereign (or sovereign-in-the-making) is that they can do things their own way which is why this weekend, Prince William became the first future King of Great Britain and Defender of the Faith to appear in an official image proudly wearing shorts.
Khaki dad shorts at that.
Over the weekend, William and wife Kate, the Duchess of Cambridge released their official Christmas card for the year, a moment that is normally notable for how predictably unimaginative and monotonous the carefully chosen image is.
For years now, the couple has stuck to a pretty standard formula of small children suitably scrubbed in a co-ordinating palate posing in a garden.
But not this year.
Instead after a stormy, trying year, the Cambridges ditched their usual tedious dedication to dull family portraits and opted for a photo taken during a holiday to Jordan.
This is not your usual royal Christmas card, not by a long shot.
William is perched on a round gold orb, Kate has clearly managed to bring trusty her hair curler to the desert and the couple's three tots all look like they have only been marginally threatened with an extended visit to Grandpa Charles' house to hear him give an impromptu lecture about 15th century Tuscan architecture. (A powerful incentive to behave if ever there was one.)
However, what really sets this apart from previous stodgy fare of this sort is not only William's casual attire but the fact that he and Kate have their hands on each other's legs, putting on the most touchy-feely display by a monarch since King Henry VIII spotted Anne Boleyn and started to get ideas.
This wasn't just a tender intimacy but a much racier, if you will, display that stands in glaring contrast to their usual reserved and restrained public demeanours.
And all of this adds up to something particularly interesting in terms of what this card reveals about what William and Kate are up to right now. That is, it highlights the degree to which the duo are showing little appetite to obediently toe the line and rigidly, blindly adhere to The Firm's status quo.
What this card really signals is the extent to which they intend to do things their own way and if that means seeing the one-day King William IV's pasty gams, then so be it.
William and Kate might be inexorably making their way towards the throne but the message that is increasingly coming across is that they intend to do it on their own terms.
In fact, over the 12 months there have been an increasing number of indications that they are busy rewriting the palace playbook.
In April, to mark their 10-year wedding anniversary they released not only the expected staid portrait of the duo but a heavily stylised, professional "home movie" that boasted the sort of production values that would put even Netflix to shame.
In May they launched their own YouTube channel, the first royal household to run their own distinct offering on the site, with a peppy introductory video showing them larking around behind-the-scenes and Kate giggling.
Later the same month, when Lord Dyson released his report into the BBC's handling of the Diana, Princess of Wales' devastating 1995 Panorama interview, William did not react by putting pen to Kensington Palace notepaper but delivering a wholly unprecedented, and emotional, statement to camera.
On the work front, the couple has been making waves too, with Kate launching The Royal Foundation Centre for Early Childhood in June and William's debut Earthshot Prize happening in October, the first of 10 such outings over a decade which will see a staggering $97.4 million directed towards finding solutions to the climate crisis.
Sure, all of this might not quite be up there with Henry VIII's decision to split from Rome in 1534 but the Cambridges have likewise been quietly adopting a distinctly heterodox and stealthily progressive approach to both their family life but their day jobs too.
What further sets this card apart it proves is that even if you have the Queen's email address (she has had one since 2007) and are a bona fide HRH, you can still enjoy an impressive degree of privacy and move around the world unmolested and without the press finding out.
While Kensington Palace has revealed the country where this shot was taken they have not divulged a single skerrick about where in the Middle Eastern nation the family was, when they were there or even what they were doing so far away from their SWI postcode. They were spied at Heathrow in October, with speculation they were off on an overseas jaunt at the time, and that could have been when this family excursion took place, but that is a guess at best.
Likewise, the Cambridges managed to get to the South of France for her brother James Middleton's recent wedding and celebrate the nuptials without a single, solitary blurry iPhone shot emerging of them.
While Diana was dogged by a predatory press pack, by and large, to be a member of the royal family today is to be able to get on with your life and to stay, by and large, under-the-radar. There has never been a photo of Kate or William at their childrens' school or of Kate at her weekly tennis lesson at the Hurlingham Club. Nor do we see shots of her shopping, getting her hair cut and spending time with her sister Pippa Mathews, all things that she regularly enjoys.
The Duchess of Cambridge manages to get on with her life and to do it without living in the eye of a media storm which is curious given that this stands in opposition to the picture cast by Meghan, the Duchess of Sussex when speaking to Oprah Winfrey earlier this year. Recounting conversations with "people within The Firm," she said she would ask,
"'Can I go and have lunch with my friends?' 'No, no, no, you're oversaturated, you're everywhere, it would be best for you to not go out to lunch with your friends'. I go, 'Well, I haven't … I haven't left the house in months.'"
There is no denying for a second that marrying into the House of Windsor is an unambiguously isolating experience that dramatically rearranges a woman's entire existence, but what Kate and William have proven time and again is that you can get on with life without your every salad, shoe shopping expedition and manicure ending up splashed across the tabloids day.
When Kate joined the royal family back in 2011, it looked like she would be about as subversive as a Philip Treacy chapeau at Ascot or a G&T surrounded by a few dorgis. Instead, she is one half of the most radical royal catalysing duo since … Henry VIII and Anne Boleyn. It's always the quiet ones, isn't it?
• Daniela Elser is a royal expert and a writer with more than 15 years experience working with a number of Australia's leading media titles.