Princess Beatrice chose a long black gown while Princess Eugenie went for bright blue at a children's charity event at The Banqueting House in Whitehall last night. Beatrice's boyfriend, Dave Clark, and Eugenie's boyfriend, Jack Brooksbank, both wore bow ties for the formal do. The couples have been enjoying double dates recently, partying at The Box last weekend alongside Rosie Huntington-Whiteley and Jason Statham. The sisters also had fun on a girls' night with Chelsy Davy and Pippa Middleton last month, after skiing with Sarah Ferguson in Switzerland. Eugenie and Beatrice have two royal weddings to attend this year: Prince William and Kate Middleton's service on April 29 at Westminster Abbey, then Zara Phillips and Mike Tindall's ceremony on July 30 in Edinburgh.