And the pretty actress looks better than ever. Sienna made her post baby comeback at the Hamptons Film Festival in a floor-length white dress with cape and cuffs.
Fashion fans recognised the lovely gown straight off – it was a shorter, caped version of the Alessandra Rich gown Gwyneth Paltrow wore for the Oscars.
Sienna picked the white hot ensemble for a reception honouring Richard Gere.
Then the following day the 30-year-old stepped out again, this time wearing a monocrome shirt and trousers combination with some funky sunglasses.
The Alfie actress welcomed a baby daughter with her fiancé, actor Tom Sturridge, in July.
Her designer sister Savannah revealed on Twitter that the new arrival is called Marlowe.