He surprised her with a very special performer ??? Katy Perry!???There was a full stage with lighting and effects,??? one of the guests tells In Touch, adding that celebrities such as Oprah Winfrey and Vivica A. Fox attended the private party on Dec. 29 at the 63-year-old talk-show host???s Beverly Hills mansion.WATCH: Katy Perry and John Mayer Debut Heartwarming New Music Video For ???Who You Lov