Naomi Watts made a dramatic transformation for her role as Princess Diana in Diana on set in London today. She sported brown locks to rehearse a romantic rendezvous scene with Naveen Andrews, who's playing Dr. Hasnat Khan. Diana and Hasnat went to great lengths to keep their relationship quiet, with Diana reportedly changing her hair color to throw off the cameras. It's a different look for Naomi, who has been filming with a blond 'do since the beginning of July. She did break from work for a family vacation to Saint-Tropez, where she and husband Liev Schreiber showed PDA during a stroll with their sons, Sasha and Kai.