Ever since the death of their mother, they have been linked inextricably, not just in the public consciousness but across the royal stage.
As boys, William and Harry were inseparable, finding solace in one another as they coped with the shattering loss of Princess Diana and later sharing in each other’s dreams and successes as adults.
William’s marriage to Kate eight years ago contributed barely a quiver to this remarkable relationship as two became three. The arrival of the Cambridges’ children George, Charlotte and Louis served only to strengthen the fraternal bonds.
When Meghan arrived with her Hollywood glamour the threesome became the Fab Four, as popular as any pop group but dusted with the magic of royalty.
But now with the news that the brothers are to set up their separate households there is a parting of the ways. Many will seize on the split as evidence of a so-called froideur not just between the sisters-in-law but also between William and Harry.