Superstar Prince has appeared on the catwalk at London Fashion Week after staging a surprise performance for designer pal Matthew Williamson's show. The Purple Rain hitmaker was a front row guest at Williamson's spring summer show when one of his songs was played over the catwalk. Prince began singing into a microphone from his seat and jumped onto the runway flanked by his band. Williamson says, "He really wanted to do this, and you don't say 'No' to Prince."