While the fleur-de-lis has featured on various European coats of arms and flags over the ages, it is historically connected with the French monarchy and continues to appear in the arms of the King of Spain and the Grand Duke of Luxembourg, both of whom are members of the House of Bourbon. Although it has never been officially adopted by any of the French republics, it is an everlasting symbol of France that appears on French postage stamps. The three leaves, according to French historian Georges Duby, reflect the medieval social classes of those who worked, battled, and prayed.