The blonde starlets joined a host of celebs to celebrate the global launch of BMW's new electric car BMW i3 at Old Billingsgate Market in London.
Sienna took a well-deserved break from baby duty to co-host the star-studded bash, and she didn't fail to impress in the fashion stakes either!
The stylista defied the dreary skies in a pretty floral sundress by Dolce & Gabbana, complete with ravishing heels by Charlotte Olympia.
She amped up her peepers with soft smoky brown eyeshadow, whilst accentuating her pout with a slick of coral lippy.
Meanwhile, fellow Brit Laura was hard to miss in a shout-out yellow dress by Motel Rocks.
The MTV presenter opted for a bumble-bee colour scheme, adding black suede courts by Kurt Geiger and a boxy clutch by Jimmy Choo.
Also co-hosting the do was James Franco, who looked dapper (and ever so handsome) whilst pulling a smouldering pose in a tailored Gucci suit.
Model Poppy Delevingne was in attendance too, but she broke from the event's cocktail dress theme and instead chose sophisticated cigarette pants by Missoni and a denim shirt by Mother.
Gosh, they're a stylish bunch!
Watch a video from the event below:
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