Sienna Miller attended the Cannes Film Festival to promote her new movie Horizon: An American Saga at the weekend and she made sure it was a family affair by bringing along her daughter Marlowe, boyfriend Oli Green and her mum Josephine.The actress, 42, arrived on the red carpet in a semi-sheer lavender gown by Chloe with layers of ruffles and a playsuit underneath, showing off her amazing figure. She accessorised it simply with a giant diamond necklace and her signature red lippy.