The trend began as far back as 2005 when the pair shared a photo of them graduating from St Andrews College and popped up again in 2010 when the newly engaged couple stepped out in matching navy outfits.
And without fail, it’s continued with the kind of consistency only the British royal family could offer.
Remember when the couple stepped outside of their maternity ward to show Prince George off to the world? Matching outfits.
When they toured outback Australia? Matching.
When they drank red wine and donned tailored blazers? Game, set, matching.
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From cowboy hats to waterproof coats, ball gowns to khaki pants, this duo has seen and worn it all. And remarkably, they do it well. Where most of us would be scoffed at or ridiculed by those near to us for some of these outfits, somehow, the future King and his wife make it look okay.
(And being a painfully pale, lanky, balding white man and making a Hawaiian shirt look okay is a skill not to be underrated.)
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Kate's block blue dress the perfect lead for William's matching tie, George's shorts and Charlotte's dress, all within the same palette.
And let's not forget Charlotte's cardigan matching George's shorts during their Canadian tour, either.
Which, when you think about it, is fitting, really, because if history has taught us anything it's that a family who dresses together stays together (the Von Trapps, I'm looking at you.)
The real problem the couple now face, though, is that should they ever part matching ways, they're almost guaranteed to be plagued with marriage rift rumours.
But for now, here's to many, many more years of matchy-matchy fashion from the royal house of Windsor.