But the 'side boob' almost stole the limelight from Jess' co-stars, Toni Collette - who'd gone blonde for the bash - and Helen Mirren, who looked immaculate in a black lace dress with gold detailing.
Jessica's dress was a bit of a show-stopper all-round, with dramatic ruffles at the front:
A stunning updo and flesh-flashing from the side:
And a sexy split and cutout feature at the back:
But all the girls managed to hold their own, and our very own Dame Helen was on particularly top form.
Who do you think won the style show? Apart from the 'boob'...