Simon Cowell Throws Himself A $1.6 Million Birthday Bash

You only turn 50 once is what Simon Cowell seems to be saying. He's celebrating Saturday night with 400 of his closest friends at a party reportedly costing $1.6 million!

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The event is happening at Wrotham Park, a Palladian mansion outside of London where a giant tent (and a separate one for smokers like the birthday boy) was erected days earlier.

Simon's American Idol pals Randy Jackson and Ryan Seacrest flew into London earlier in the week and were out clubbing Friday night.

Paula Abdul was uncertain about going because of the flu.

The guest list includes Simon's good friend Sir Elton John who may perform alongside Cowell's musical discoveries Leona Lewis and Il Divo. Others expected are Simon's ex-girlfriend, Terri Seymour of TV's Extra, supermodels Naomi Campbell and Kate Moss, AI make-up artist and Simon's

good friend Mezhgan Hussainy, and Simon's beloved "mum" Julie Cowell.

Read Simon's Letter To Himself, Written On The Eve Of His Birthday.

Simon's actual birthday is Wednesday.