Most of Catherine Schell's (Lady Litton's) laughter is genuine. Peter Sellers (Inspector Jacques Clouseau) made her laugh so hard once the camera was rolling, she had a real problem keeping a straight face in many of her scenes with him. This resulted in writer, producer, and director Blake Edwards giving up on trying to get her to react like she was supposed to in the script.
Dame Julie Andrews filmed a cameo role as a maid removing the unconscious Inspector Jacques Clouseau (Peter Sellers) from Lady Claudine Litton's (Catherine Schell's) room, but her part was edited out.
Douglas Fairbanks, Jr. was offered the role of Sir Charles after David Niven proved to be unavailable. After some consideration, he turned it down, paving the way for Christopher Plummer.
Unlike the other movies in the original Pink Panther film franchise, United Artists was not directly involved in the making of this movie. Because the careers of writer, producer, and director Blake Edwards and Peter Sellers were declining, United Artists had no desire to finance another Panther movie. Edwards took his script of this movie to British producer Sir Lew Grade, who subsequently bought the rights. Grade financed this movie himself, while giving United Artists worldwide distribution rights, ownership in the copyright, and a stake in the profits (as they owned the characters) in order to make the movie. Distribution rights in later years reverted back to Grade's company, ITC. This is the reason why, until recently, this movie had not been featured in compilation DVD box sets along with the other Panther movies. United Artists (via MGM) has since reacquired domestic rights to this movie and it has now been issued in a Blu-ray box set of all of Sellers' "Pink Panther" movies, while international rights are now with Universal Pictures.
This movie was originally intended to be a 26-part Pink Panther mini-series produced by writer, producer, and director Blake Edwards for the British ATV. The ATV then decided to turn it into a "movie-of-the-week", followed by a move to a feature film.