At the first ball, the song Jane is dancing to is "The Boy Next Door." The song is from Meet Me in St. Louis, also directed by Vincente Minnelli.
For years John Saxon said he had been bothered by something about Sandra Dee during filming that he just couldn't put his finger on. Decades later he figured out what it was - because she'd lied about her age, she was only 14 years old.
The film was shot in Paris because Rex Harrison was having tax problems and could not go to the U.S. or the U.K.
The original Broadway production of "The Reluctant Debutante" by William Douglas-Home opened on October 10, 1956 at Henry Miller's Theatre, ran for 134 performances and was nominated for two 1957 Tony Awards for acting. William Douglas Home also wrote the screenplay on which the movie version was produced.