Where: At the 20th Hamptons International Film Festival in Long Island, New York, for the premiere of The Girl.
What: She only gave birth to daughter Marlowe in July, but Sienna was showing off a stunning slim figure in crisp white column dress with cape-like sleeves.
The actress accessorised with beautiful gold cuffs, a tiny red clutch bag (they do say the best things come in small packages), and finished off with extremely natural make-up.
Verdict? A triumphant return to the red carpet... what say you?
See more Sienna style here: