Marlon Brando was scheduled to co-star but bowed out after reading the script which he considered mediocre at best. He was replaced by Frank Sinatra.
Cary Grant considered himself to be miscast in this film.
By all accounts, Frank Sinatra was at his most obstreperous throughout the making of this film. Among other things, he refused to use the car supplied him by the studio, insisting upon having his Ford Thunderbird flown all the way to Spain at the studio's expense. In addition, he almost caused an international incident when he hung a banner from his hotel room window reading "Franco is a Fink", referring to Spain's dictator, Francisco Franco. In hindsight, Sinatra referred to the whole experience as "underwhelming".
Earl Felton's uncredited re-writes were the subject of Mike Walker's play "The Gun Goes to Hollywood", broadcast on BBC Radio 4 on 14 March 2011.
In an attempt to improve her lingual skills, Sophia Loren underwent a crash course in English on the advice of then agent (and husband-to-be) Carlo Ponti.
Loren received a reported $200,000 for her work on this production, the publicity stills of which, were taken by Kenneth Danvers.
The film's screenwriters, the team of Edna and Edward Anhalt, were in the process of terminating their marriage, which may account for some of the inconsistency in the script.
This was one of two films Sophia Loren and Cary Grant starred in together. Cary was totally in love with Loren and the two had an affair. However, Cary was too much in love with Sophia to the point of obsession. This frightened her and sent her straight into the arms of Carlo Ponti.
With seven weeks of shooting in Spain still left on the schedule Frank Sinatra, who hated Spain, told Kramer, "Hot or cold, Thursday I'm leaving the movie. So get a lawyer and sue me," according to Kramer biographer Donald Spoto. Kramer tried to solve the problem with two days of shooting in a Hollywood studio with potted palms.