The real Anthony Drexel Biddle, Sr. (1874 - 1948), was a banking magnate and dyed-in-the-wool eccentric whose independent wealth allowed him to pursue such diverse ventures as physical culture (he boxed with Jack Johnson and taught boxing to Gene Tunney), theatricals, and religion. He served as a Colonel in the U.S. Marines in both World Wars. Neither was Cordelia Biddle Duke's marriage to Angier Buchannan Duke to result in the happy ending the movie implies. Although they had two sons, both of whom became prominent in business and diplomatic circles, the marriage ran into trouble, they were divorced within a few years, and Angier Duke died young, not long after that, in a boating accident.
The last live action film that Walt Disney worked on. At the time of his death, the crew had completed principal photography, but post-production had not begun. It was with this film that the studio's trend of subjecting its live-action musicals wholesale cuts began. Radio City Music Hall, the site of the film's New York premiere, had a Disney-themed Christmas stage show and demanded cuts to accommodate it.
The song "Fortuosity" was written for Tommy Steele, who sings the song in the movie. It replaced a song called "Off Rittenhouse Square," a demo of which appeared on the film's CD soundtrack reissue in 2002.
Cordelia Biddle Duke Robertson (1898 - 1984) co-wrote (with Kyle Crichton) the book upon which both the movie and play "The Happiest Millionaire" were based, "My Philadelphia Father." After her divorce from Angier Buchanan Duke (who, unlike his character in the movie, was actually more than a decade her senior), she made a far happier marriage to architect Thomas Robertson, a marriage which lasted until his death in 1962. Like her father, she enjoyed an active life devoted to many charitable activities. By most accounts, she was one of those women who grew more attractive as they grew older, prompting a reporter to state "The aura of youth clinging to this illusion. It is no product that can be bought in a beauty shop or designer's salon. Hers is a youth that laughs at the insolent years..." Active almost to the end of her life, she died at her home in Southhampton, New York.