Daniel Massey played Noël Coward, his own godfather. Massey made his theatrical movie debut as a young boy, playing Noël Coward's son in the wartime drama, In Which We Serve (1942).

Dame Julie Andrews and Gertrude Lawrence have much in common: both were born in London; performed in music hall as children; and became box-office stars after their first American shows.

After this musical flopped at the box-office, Twentieth Century Fox decided to substantially cut and re-market the movie. They did some primitive market research, and tested audience response to three titles: "Music For The Lady", "Star!", and "Those Were the Happy Days". The latter got the best response, but (possibly to avoid confusion with a couple songs about happy days) the final title was "Those Were the Happy Times". Executive Producer and Director Robert Wise didn't believe revamping this movie would work, but he didn't interfere. He declined to be involved in the re-cutting and asked that his credit "A Robert Wise Film" be removed. Original Editor William Reynolds was hired to cut down this movie based on instructions from Richard D. Zanuck. The cuts were a bad idea, but they were very adeptly done. They hired the same artist who did the poster for The Sound of Music (1965) and every attempt was made to make audiences think this two hour version was a similar movie. The original title was tucked into a corner of all of the ads, so audiences were not fooled, and this desperate effort only convinced people who hadn't seen the original that it really was a bad movie. By the time it debuted on American television, the original title was restored, but the movie was still cut. At almost the same time, it debuted on television in England, but in the full original version, missing only the overture and intermission.

Jewelery worth one thousand two hundred fifty pounds sterling was provided by Cartier for Dame Julie Andrews to wear, and on every occasion, a Pinkerton detective was on-duty.

Dame Julie Andrews' wardrobe (designed by Donald Brooks) set a record for the largest number of costumes for an actress in one movie, at one hundred twenty-five.

This movie grew out of a massive attempt by Twentieth Century Fox to duplicate its earlier success with The Sound of Music (1965) by producing three expensive, large-scale musicals over a period of three years, Doctor Dolittle (1967) and Hello, Dolly! (1969) being the others. Unfortunately, tastes in popular entertainment were beginning to change, and all three movies' box-office performance reflected this. All were released amidst massive pre-release publicity and all lost equally massive amounts of money for the studio. The result was that several top studio executives lost their jobs, and the studio went into such dire financial straits that it only produced one movie for 1970. In truth, it would never recoup its losses until a highly successful theatrical re-issue of The Sound of Music (1965) in early 1973.

According to a Dame Julie Andrews' biography, Sir Ian McKellen screentested for the role of Noël Coward by performing Coward's own "Parisian Pierrot" and received an ovation from William Fairchild and the crew. However, he lost out to Daniel Massey.

The final camera slate number was "1417", close to the then all time record for a musical. Dame Julie Andrews appeared in one thousand three hundred six of them, which was then a record.

Apart from Richard Aldrich, a certain amount of dramatic license was taken with the men in Gertrude Lawrence's life. In the movie, her first husband, a stage manager, is called "Jack Roper", and is apparently not much older. In real-life, his name was Frank Gordon-Howley, and he was twenty years older than her. Her upper-class, Guardsman boyfriend was not called "Sir Anthony Spencer", but Captain Philip Astley. He later married Madeleine Carroll. The Wall Street banker she met while on Broadway was named Bert Taylor, not "Ben Mitchell".

Beatrice Lillie was a friend of Gertrude Lawrence, but her role was written out of the screenplay after she refused to let anyone play her role but herself (she was seventy-three at the time).

Peter Cook and Robert Stephens were in the running to play Noël Coward.

Three thousand forty individual costumes were produced at a cost of three hundred fifteen thousand pounds sterling. Dame Julie Andrews wore one hundred twenty-five different outfits costing one hundred forty-four thousand five hundred pounds sterling, including ninety-six different gowns.

Dame Julie Andrews agreed to star September 4, 1964 before a line of the script had been written. One thousand one hundred ninety-seven days later was the last day of shooting.

The origins of this project date back to 1955, as a musical/drama vehicle produced by Warner Brothers for Judy Garland, and as a follow-up to her triumph in A Star Is Born (1954). After Garland lost the Academy Award for Best Actress that year, in addition to the hatred Jack L. Warner had working with Garland and Producer Sidney Luft during the movie's production, all future projects between Transcona Productions (the production company set up by Garland and Luft) were abandoned and her three-movie contract cancelled.

Filming took one hundred forty-nine shooting days.

Eighteen stars and principal actors and actresses were backed by one hundred forty-four speaking actors and actresses, one hundred seventy-eight bit players and nine thousand eight hundred forty-seven background players, with about six hundred twenty used in a single sequence.

Six thousand eight hundred fifteen hand prop items were made to order or obtained from antique shops.

One hundred eighty-five sets were built for this movie.

Judy Cornwell was offered a key role.

Dame Julie Andrews' contract for The Sound of Music (1965) required her to do a second movie for Twentieth Century Fox. Executive Producer and Director Robert Wise and Producer Saul Chaplin were so impressed with Andrews that, as they were completing The Sound of Music (1965), they knew they had to take advantage of this by doing another big musical in which to cast her.

More than five hundred thousand feet of film was shot.

Features Daniel Massey's only Oscar nominated performance.

Bruce Forsyth, who played Gertrude Lawrence's father, was only seven years older than Dame Julie Andrews.

Adding to the enormous cost of this production was the decision to shoot in the very expensive Todd-AO process for 70mm release.

To insure the quality of their expensive big budget musical, Twentieth Century Fox hired some of the people responsible for some of the classic MGM musicals including Producer Saul Chaplin, Choreographer Michael Kidd, and former MGM Music Director Lennie Hayton.

During the cricket match in the alley, there is a line "If that was a googly, I'm a Chinaman." In cricket, a "googly" is type of delivery bowled by right-handed leg-spinner, where the ball moves into the batsman rather than away from him. It is also called a "wrong'un". (Note: left-handed spin bowlers are sometimes called "Chinaman" bowlers.)

Ballard Berkeley is credited by several sources as having been in this movie, but he did not actually appear.

Roger Delgado, the actor who would later originate the role of Doctor Who's nemesis "The Master", is seen briefly as a visiting French diplomat passing by the (censor) Lord Chamberlain's office, aghast at overhearing "Noël" and "Gertie" straddle each other while rehearsing a scene from Coward's play "Private Lives" (to show the censor firsthand that it was going to be suitable for public taste.).