It is certainly true that there has been a strong tradition of kilt wearing by royal males, at least when they are in Scotland, since the days of Queen Victoria.

But that tradition would seem to be no longer as strong, apart from Charles among the Queen's sons and Andrew and Edward are much less frequent kilt wearers.

Even studying at St Andrews did not make William any more desirous of wearing the kilt, and although there was the moratorium on him being photographed by the press no stories of occasions when he might have been kilted have come to light that I know of.

And even at Balmoral William and Harry have not followed the established tradition.

So where they have a choice it appears bifurcated garments are what they go for.

Only stern duty, when it cannot be avoided in the future, would appear to bring about them donning a kilt. This is unlikely to be until William becomes Duke of Rothesay and in the case of Harry should he be given a Scottish title.