Cary Grant was 53 when he made this film; his romantic lead, Sophia Loren, turned 23 during shooting.
The original screenplay was written by Betsy Drake, Cary Grant's wife at the time. Grant originally wanted it to star her, but his extramarital affair with Sophia Loren complicated the project. Grant decided to have Loren replace Drake. Adding insult to injury, it was drastically rewritten to accommodate Loren by two other writers, Jack Rose and Melville Shavelson (who also directed). Bearing little resemblance to her original script, Drake received no writing credit, and the reworked script was Oscar®-nominated for Best Original Story and Screenplay.
Cary Grant initially accepted his role because he was dating Sophia Loren, with whom he was madly in love. After she married Carlo Ponti in September 1957, a heartbroken Grant wanted to back out. He couldn't, but the director made sure the production was a smooth one.
Carlo Ponti obtained a Mexican divorce from his first wife and married Sophia Loren by proxy, while she was shooting this film and dating co-star Cary Grant.
Sophia Loren performs a novelty song, "Bing! Bang! Bong!" In 2015, her version of the song was used in a heavily rotated UK TV commercial for Twinings teas.