Best known for Downfall, about the last days of Hitler, director Oliver Hirschbiegel turns his attention now to a cuddlier if thematically consistent subject: the last years of Diana, Princess of Wales. This inessential but watchable and poshly mawkish movie covers the brief span between her divorce from Prince Charles and her 1997 death in a Paris car crash with Egyptian billionaire scion Dodi Al Fayed — two events whose exposition Hirschbiegel willfully shirks in favor of dwelling on Diana’s intense semi-secret romance with Pakistani-born London heart surgeon Hasnat Khan. Here she takes the form of a carefully coiffed and costumed Naomi Watts, and he’s played by Naveen Andrews, from Lost and The English Patient. Both are charming and commanding; they maintain their dignity even when the dialogue creaks, which is often. Playwright Stephen Jeffreys’ script adapts Kate Snell’s book Diana: Her Last Love, and sets the proceedings within a misty cloud of conjecture. It’s all very romantic and sometimes ridiculous. (And it feels a little dodgy that her kids, Princes Harry and William, are sequestered offscreen, albeit ostensibly for their own protection.) Also, being a princess story, Diana does nuzzle its way into fairytale indulgence, now and then exuding less fealty to the woman herself than to old Audrey Hepburn movies — which wouldn’t be a bad way to go if Jeffreys and Hirschbiegel had better tempered it with subtlety and self-awareness, or at least something new and vital to say.