Twilight star Kristen Stewart is set to play Princess Diana in a new period drama about the Royal's life, an intriguing casting choice that set social media ablaze on Wednesday.Kristen, 30, has signed on to the movie Spencer, that will dramatize a 'critical' weekend in the early 1990s, when Diana decided that her marriage to Prince Charles wasn't working, Deadlinereports.However, many were quick to react negatively to the news on on Twitter, with users joking: 'What could possibly go wrong?' while another said: 'Couldn't you have found a British actress?' Royal role:Kristen Stewart will play Princess Diana in new biopic Spencer...