I'm fortunate enough to be personally acquainted with a couple of Imperial Highnesses here. Having a tiny dash of blue blood coursing through my own veins (some remnants from a a very distant crusader in the XII Century, carried on by a few noble if promiscuous medieval gentlemen of the Clergy), I seem to have a built-in "nobility sonar". These ladies are indeed regal in pose, manner, and disposition. Thus any garments they wear are "nobled" in turn by their wearer. This is such a Gown. Exclusive to Royalty. (Bowing out)