Being a working member of the royal family is a role that annoyingly comes without a job description. (Just ask Meghan, the Duchess of Sussex who admitted to Oprah earlier this year, "I didn't fully understand what the job was.")
As all the women who have married into the monarchy over the last century, including Diana, Princess of Wales, Sarah, the Duchess of York, Sophie, the Countess of Wessex and Kate, the Duchess of Cambridge have learned painfully, the only way to fully get a grip on being a card-carrying representative of the Queen requires fairly brutal on-the-job experience and running the PR gauntlet.
Here's the "but" – the upside of that lack of formal prescriptiveness is, handily, there is no such a bourgeois thing as any sort of cap on holiday leave. Mustique for some sunshine and one of Basil's Bar's delightful pina coladas? (Kate's go-to tipple there FYI.) Of course. A quick Verbier dash for some off-piste action? Lovely. A week of salmon-fishing, grouse-hunting and whiskey-fuelled charades? Sounds like just the ticket.
However, not even this loosey-goosy approach to vacation time quite explains the current mystery surrounding Kate, the Duchess of Cambridge.
Where the dickens is she?
As of today, the royal has not been photographed or taken part in any public engagements for 58 days.
The last time the royal was in the public eye was on July 11 when she attended Wimbledon men's singles final before a costume change and zipping across London for the Euro 2020 final at Wembley with her husband and son Prince George. (The poor little poppet is probably still in his bedroom mournfully clutching onto his Three Lions stripe and wondering where it all went wrong.)
Last year, the longest gap between public appearances (including Zoom engagements) was 41 days. On August 5, she and William visited Wales, spent much of the month on a break, and then she reappeared for a series of outings in London on September 15.
In 2019, that figure was 33 days but that also took into account nearly the whole month of August, when the entire royal family's out-of-office is on.
For the last two years, she and William have also undertaken an engagement early in the month (taking part in the King's Cup Regatta and visiting Wales respectively) but not in 2021.
Their social media accounts don't offer any clues.
The last time Kate was seen on their official Instagram account was also on July 11 at Wimbledon. (On August 6, a photo showing Kate with Holocaust survivor Steven Frank and his granddaughters was posted, however it was taken in January 2020.)
Last week, marked the beginning of the new school term which would have seen Prince George and Princess Charlotte return to their school Thomas' Battersea.
In some previous years, Kensington Palace has marked the occasion by releasing official photos of the Duke and Duchess doing the most stage-managed version of the school run known to man.
Not this year.
(To be fair, William and Kate do actually do the school run every day and are by all accounts as normal parents as they can be. Kate reportedly queues with other parents in the morning to grab a coffee and in 2019 it was revealed that her protection officers had snuck her into a Chelsea pub so she could join other parents for meet-and-greet drinks.)
To be fair, July and August are typically fallow periods in the royal calendar.
Like the rest of the UK who (during normal times at least) spend the summer months trying to flee the country en masse for a week in Malaga, the royal family is equally as committed to getting away for their summer hols. (Only we're talking Balmoral, not Benidorm; laphroaig not lager; and midges not Midori-fuelled make-out sessions.)
Still, even the Windsors' usual penchant to spend the last month of summer soaking up the lack of Scottish sunshine and dodging Princess Anne when she enthusiastically comes bearing the dog-eared family copy of Trivial Pursuit does not entirely explain Kate's AWOL status.
Like a sort of blow-dried Loch Ness monster, there have been a number of sightings of the 39-year-old in recent weeks.
In early August, it was reported that William, Kate and their three kids were indulging in a getaway on an island in the Cornish archipelago, the Isles of Scilly.
Later the same month, reports emerged that the Cambridge family had made their annual pilgrimage north for a Scottish getaway.
"They always enjoy going up to Balmoral, they love the outdoors and walking in the hills and spending quality time with family," a source told Vanity Fair's royal editor Katie Nicholl. "It's where William spent a lot of his childhood and it's important to him that his children experience what he did as a young boy."
On the agenda for the energetic family – walking, fishing, riding and cycling. (No lolling about in front of Moana here.)
Then last week, Vanity Fair also reported that, per a source in Norfolk where the Cambridges have their country estate Anmer Hall, William and Kate have been busy teaching their kids the difference between a jib and a spinnaker.
"They are very much a family of sailors now," a source said. "They have enjoyed some wonderful time on the coast this summer sailing and showing the children how to steer and sail a boat. They love the water and the two eldest are good swimmers and had no qualms about jumping into the sea even if it was a bit fresh."
Given we have proof of life here, so to speak, and we know she has not accidentally locked herself in the Queen's tiara vault, what might be going on?
There is, of course, the "p" word – pregnant. Could there be any chance that the 39-year-old is expecting baby number four?
An intrepid royal sleuth armed with nothing more than problematic Wi-Fi and a lot of time would have to go back to 2017, when Kate was suffering from hyperemesis gravidarum aka acute morning sickness again, to find a break in the Duchess' schedule that was quite so lengthy.
Short of getting access to a remarkably accurate crystal ball or a royal urine sample, we will just have to play the waiting game here. However, if this is the case and there is another adorable Cambridge tot on the way, we may very well hear about this soon. Kate's second and third pregnancies, with Charlotte and Louis, were announced in September.
What this current mystery highlights however, is how unusual this break is for Kate and how much she has put on her plate in recent years, notably with her focus on her Early Years initiative ramping up and launching the Royal Foundation Centre for Early Childhood in June.
This is a trend that is likely to continue as both she and William take on more responsibilities and assume more of the burden as the Queen inches closer to hitting the big 1-0-0.