Nigel Hawthorne (Lord William Lamb, 2nd Viscount Melbourne) previously played Queen Victoria's grandfather King George III in The Madness of King George (1994).
Jonathan Cecil, who plays a servant of Queen Victoria, is the great-grandson of Queen Victoria's last Prime Minister Lord Robert Gascoyne-Cecil, 3rd Marquess of Salisbury.
Jonathan Firth played Prince Albert, namesake of the subsequent Prince Albert/King George V, played by his brother Colin Firth in The King's Speech (2010).
Peter Ustinov previously played King William IV's elder brother, the Prince of Wales (the future King George IV), in Beau Brummell (1954). In the interim, he played their great-nephew King Edward VII, Queen Victoria's eldest son and eventual successor, in Strumpet City (1980).