On the first Monday in May, the fashion cognoscenti descend on New York’s Metropolitan Museum of Art for the most glamorous event on the fashion calendar, the Met Gala. Attracting the likes of front-row frequenters, up-and-coming models, Hollywood A-listers and fashion royalty, it has also seen real royals walking the famous Met steps. From Princess Diana’s show-stopping moment in John Galliano’s first design for Dior, to Princess Beatrice’s more recent foray into Grecian ball gowns courtesy of Alberta Ferretti, here are the moments when the royals went fashion…