Paul Bettany was cast as Lord Melbourne despite being roughly twenty years too young for the part. Vallée explained, "We couldn't find a 58-year-old actor who was sexy and good-looking enough. Paul was a more than good enough actor to age from the inside, and he plays him as a great politician and a great seducer." Early in the casting process the crew wanted to cast Miranda Richardson as the Duchess of Kent, and believed she had such great chemistry with Blunt that it became "genuinely uncomfortable watching them in a scene, as the scenes are so intense and real." Jim Broadbent and Mark Strong joined the cast as King William IV and Sir John Conroy, respectively, as did Harriet Walter as Queen Adelaide. Sarah's elder daughter, Princess Beatrice of York, made her film debut in a small cameo role, becoming the first member of the Royal Family to appear in a non-documentary film.