The film featured, as the credits read, "the singing voice of Mario Lanza". Lanza had originally been cast as Prince Karl, but the singer was fired from the picture (some sources state that Lanza voluntarily walked off the film). Under the terms of the eventual settlement between MGM and Lanza, the studio retained the rights to use the songs for the film's soundtrack that Lanza had already recorded. The songs (including "Beloved" – written specially for the movie – and the well-remembered "Serenade", from the original show) would become some of those most identified with Lanza, even though they were mouthed in the film by Edmund Purdom, who took over the role of Prince Karl. Ann Blyth co-starred as Kathie. Blyth had played opposite Lanza in the 1951 blockbuster "The Great Caruso".