Prince William may not be a London Fashion Week attendee, but Prince -the musician - just performed at the Matthew Williamson show. He started off singing from his front-row seat, and then got up and joined his band--and backup danceres--at the start of the runway. What did Behati and Tanya stomp the catwalk to? "Don't have to be rich." The only problem? You DO have to be rich to wear a Williamson outfit! And royally so!