The yummy mummy-of-one led the glamour at the British Film Institute Gala Dinner and Auction, held at 8 Northumberland Avenue in London.
Sienna sizzled in a sophisticated white frock, featuring delicate spaghetti straps and a nipped-in waist. She teetered along in sky-high courts by Christian Louboutin, keeping her jewellery minimal and her nails bare.
Her golden locks were styled in a no-fuss bun and she went for simple make-up, adding lashings of mascara and petal pink lips.
Sienna's fiancé Tom Sturridge was noticeably absent from the event, but she had oodles of famous faces to keep her company instead.
Other attendees included Eliza Doolittle, Richard E. Grant, Jonathan Ross and Arsenal boss Arsène Wenger, who all turned out to celebrate British film and film talent.
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