When Anna Wintour stepped on to the stage of the David Letterman show earlier this week, there was little surprise that she was still wearing her trademark sunglasses. The famously aloof editor-in-chief of American Vogue confesses that she uses accessories as armour, and the sunglasses, allied with her fiercely-bobbed hair, serve to perpetuate her image as a controlling, inscrutable figure who is routinely described as the most powerful player in the $300bn fashion industry.

Yet as she sat down with Mr Letterman, she took the glasses off and placed them on his desk. It is inconceivable to think of this casual gesture as anything but a carefully choreographed signal: we were about to get something of the real Anna, the aura of mystery laid aside for a few precious minutes.