SUPERMODEL Kate Moss is planning to surprise her friend/media mogul Simon Cowell on his 50th birthday by singing a song at his party. Apparently, the beauty is thinking of a couple of songs to choose from. Its a toss up between a Marilyn Monroe-style 'Happy Birthday, or her speciality Lily Allens 'Not Fair, which she has been practising with her friend Lily, Contactmusic quoted a source as telling the Daily Star. The American Idol host has reportedly invited 400 celeb friends to the black tie bash at Hertfordshires Wrotham Park on 7 October. Sir Elton John and his partner David Furnish, Hollywood actor Kevin Spacey, actress Denise Richards, Australian pop star Kylie Minogue are some of the big names that are expected to drop in. Kate may find herself singing with the likes of Leona Lewis, who may turn up too. Simon and Kate have been friends for several years. TOI