The 35-year-old, who plays the lead characters wife Nina Fawcett in the movie, showed off her lithe legs in the flirty mini dress as she opted to accessorize with a beige clutch and gold sandals.
Her make-up was subtle but flawless as she styled her hair in messy beach waves.
Charlie Hunnam, who is the lead in the film, looked dapper in a black suit as he showed off his blonde stubble and sun-kissed complexion.
Tom Holland made a sharp appearance too, opting to wear a dark grey suit, matching shirt and black tie.
The Geordie actor admitted that he didn’t spend much time prepping for his role as he’d just wrapped Guy Ritchie’s King Arthur movie, but previously said there was a ‘real distance’ between them on set.It was just the two of us in the hotel.’ After the pair were pictured having a laugh at the recent premiere, Charlie has backtracked on the ‘silent treatment’ vibes.‘I started playing this game with Rob and he just started playing it right back,’ he said.Celebrities from Amal Clooney and Kendall Jenner to Rihanna and Cameron Diaz - they're all rocking this fabulous designer.If you're keen on Sienna's boa print bikini, click right to snap it up now or head to the carousel to bag one of our s-s-s-s-super snakey alternatives!I wanted these relationships to evolve naturally on screen.