What? Proving she really is a yummy mummy in a print-perfect purple, red and white Peter Pilotto minidress, Sienna wowed on The Jonathan Ross Show on Saturday night, where she revealed her godmother accidentally bought her a pair of crotchless knickers from Agent Provocateur and, soon after, she got pregnant...
Sienna was joined on the show by Jamie Oliver - who helped her and Ellie Simmonds cook up some festive treats - Michael McIntyre, Charlotte Church and Sheridan Smith.
Where?The Jonathan Ross Show Christmas Special, 22 December.
Verdict? We love the tousled bun and slightly hippy-ish look on Sienna. Do you agree? Leave a comment below and see more Sienna here: