It was hard not to read it as a deliberate dig. Only days after Harry and Meghan made headlines for their four private-jet journeys in less than a fortnight, William and Kate were photographed boarding a budget-airline flight from England to Scotland.
Kate carried her youngest child, Louis, across the tarmac for the early morning flight from Norwich, while William went ahead, young George and Charlotte trailing behind him. Six-year old George just about carried his own backpack, but otherwise his dad was lumbered with all the carry-on bags.
It looked utterly ordinary, even if they were boarding after everyone else and were being escorted to the plane. They are the future king and queen, after all. Even when you're taking a reported £73 flight from one unglamorous destination to another.
The relatable dullness of Prince William's domestic scene was so at odds with all the noise around Harry in the previous days. This racket included bashing of Harry and Meghan for the perceived hypocrisy of their several trips on private jets despite their noisy environmental activism; celebrity defences of the couple and accusations of racism at the root of the backlash and the intercession of Elton John, who supplied the Sussexes with both his jet and his holiday home.
It was all such a fuss, which seems to be what Meghan and Harry stir up constantly, while at the same time protesting their passion for a quiet life. And then, in contrast, there was William, quietly lugging his kids' bags and having his long legs cramped alongside his subjects.
If it was a deliberate dig by the Cambridges at the Sussexes, it was effective. At least from a public opinion point of view. Whether Harry and Meghan will pick up on that is another matter.
Earlier last week, Harry and Meghan were photographed with baby Archie, boarding a private jet to fly home from a few days in Nice. They had previously been reported to have spent several days in Ibiza for Meghan's 38th birthday, at an exclusive and expensive retreat, to which they flew on another private jet.
The optics were poor, considering the couple's exhortations in the Meghan-edited issue of Vogue that every one of us should do our bit for the planet. Harry even went so far as to explain that he and Meghan plan to have only two children, to reduce their family's carbon footprint.
That must have been music to William's ears and to those of his three children.
Soon after suggestions of hypocrisy, that Harry and his small family should need a plane to themselves, Meghan's friends rowed in to the rescue. Her best friend, stylist Jessica Moroney, ascribed it to "racist bullies". British actress Jameela Jamil said it was all down to the fact that Meghan is black and that there is an issue with the white prince marrying a black woman.
So it's not about the apparent contradiction of positioning themselves as environmentalists - and enjoying that publicity - but choosing to travel on a large plane adapted for 12 people to fly luxuriously and without the rabble. Nope, no way.
Anyway, Elton John put that accusation to rest by assuring us that it was his plane, flying them to his house and that he had made a contribution to a carbon-footprint fund to offset the environmental effect. Later, Greenpeace UK's chief scientist said that this does not amount to a "meaningful response" to the problem of aviation emissions, which did not help the image of the Sussexes as all posture and no practice.
Meghan's supporters also made the point that it is plain for anyone to see that she and Harry can't fly with the public. It would be dangerous for them, and it would be dangerous for the public. Also, said Sabrina Dhowrie, wife of actor Idris Elba and friend of Meghan, as she defended them on UK TV, people such as the Sussexes can't fly on commercial flights for fear of selfies. This is a couple, let's not forget, who value their privacy.
The problem is that Harry and Meghan value their privacy when it suits them. They want to be role models, they want to share their very modern messages about empowerment and inspiration and environmental awareness. They want to be a new kind of royal while also being the old kind of royal, who has the bottomless pit of public cash to do up the "cottage" and who flies on private jets.
The message they don't seem to be getting is that you can't have it every way.
Their new kind of royalty has come to be seen as lecturing, precious, self-indulgent and strangely short-sighted. They come across as people who will listen to no one. They are in an echo chamber of two, it appears, and doing themselves no favours.
Funnily, all of this air-travel fuss and nonsense occurred in the same week as William and Harry's uncle, 'affectionately' known as Airmiles Andy, has also been in the press for all the wrong reasons. His friendship with the late Jeffrey Epstein has done him no favours, though Andrew denies all knowledge of under-age sex slaves and his friend's proclivities.
Last week, however, an American book agent was quoted as seeing him have a foot massage from a Russian woman, while Epstein had the same. That claim was one thing, but what struck a chord was the agent's recollection of Prince Andrew's alleged whinging about his position in life. Prince Albert of Monaco, he is reported to have complained, could do what he liked without any fear of criticism, while poor old Andy couldn't budge without being slated.
As is often the case with Prince Andrew, the only answer to that was, oh, poor pet.
Harry, if he's not careful, could end up the same way, a figure perceived as ungrateful and entirely out of touch.
Meanwhile, wily old-school William racks up the brownie points. He brings his kids to school, he says he won't care if they are gay, he flies them economy on their holidays. Now that's really laying down example to the next generation. And laying it on the line to Harry.
For whom, the way things are going, it might merely seem like some public declaration of war for hearts and minds. Whether he can clearly see who's winning is the problem.
The feud between the Cambridge and Sussex families reportedly began when Harry berated his brother Prince William and sister-in-law Kate Middleton for not supporting his new wife Meghan Markle.