Where? Watching the Cartier Queen’s Cup Final at Guards Polo Club, Windsor.
What She’s Wearing: Dolce & Gabbana everything, with the main event being a £1,300 sundress.
Bridie Wilkins, Fashion News Assistant says: Swapping floaty boho for la dolce vita, actress Sienna is a summer style dream. Ladylike but far from twee, getting my hands on a punchy print frock is now my top priority.