Kristen Stewart waved to fans on her way into BBC Studios in London today. Her Snow White and the Huntsman costar Chris Hemsworth followed behind for their appearance on Radio 1. Kristen and Chris have been busy with press for SWATH since last week when they arrived in the UK. They sat for interviews over the weekend and stepped out for the big red carpet premiere yesterday. The promotional tour didn't stop Kristen from celebrating her boyfriend Robert Pattinson's birthday on Sunday, since she apparently attended his party at Claridge's. They were together again last night to fete Elle cover girl Kristen's big day when they met up at Quo Vadis restaurant.