A Royal Affair features a Swedish actress, Alicia Vikander, and a Danish actor, Mads Mikkelsen, who are already well known in America, but they almost get the film stolen out from under them by Mikkel Boe Følsgaard, a young Danish actor unknown on this side of the Atlantic. The film, as its title suggests, is a romantic historical drama. It's based on the story of the arranged marriage of Princess Caroline Matilda of Great Britain (a sister of George III) to King Christian VII of Denmark, and her affair with the king's adviser, the German physician Johann Friedrich Struensee, a story that, as the film is careful to point out, is an analog to the story of Guinevere, Lancelot, and Arthur. It's a rough analog, because unlike Arthur, Christian (Følsgaard), was quite mad. And except for cuckolding the king, Struensee (Mikkelsen) is really more Merlin than Lancelot to him -- a physician who tries to temper Christian's madness but also a political adviser determined to bring the ideas of Locke and Rousseau and other Enlightenment thinkers to feudal, priest-ridden Denmark. Director Nikolaj Arcel and co-screenwriter Rasmus Heisterberg naturally gravitate more toward the romance than the politics, using as their primary source a novel by Bodil Steensen-Leth that tells the story from the point of view of Caroline (Vikander), who is as disgusted with her mad husband as he is indifferent to her. Vikander is splendid in the role as she goes from naive enthusiasm at the idea of marrying a king, even though she's never seen him before they're wed, to icy disillusionment and from indifference to Struensee to passion. Mikkelsen is a little stolid in his role: He communicates Struensee's passion for Enlightenment ideas better than he does his passion for Caroline. But Følsgaard has a grand time playing the mercurial Christian, who is sometimes plausibly sane and even likable, but mostly acts like a four-year-old in a grown man's body, with the additional danger of having the royal prerogative to do what he wants. Arcel does a good job of rising above the clichés of the genre, and cinematographer Rasmus Videbæk and production designer Niels Sejer do justice to the handsome settings, most of them in and around Prague.