Cary Grant (Sir William Rutland) retired from acting after this movie because, at sixty-one, he had become too old to play the romantic lead. Grant, furthermore, did not think his fans would want to see him playing supporting roles.
In some scenes, Cary Grant whistles the theme music from Charade (1963) and An Affair to Remember (1957), two of his previous movies.
When Haversack is recounting his life story to Sir William in the hotel, two Victorian photographs can be seen on the desk. The portraits are of Elias and Elsie Leach who were Cary Grant's parents.
Some viewers might miss this but two of the minor roles were played by actors who had a turn of good fortune the following year. The police captain was played by George Takei, which was one year before he was cast in Star Trek (1966). Also, there is Teru Shimada who played Aiko's father. This was one year before his prominent role as the evil president of Osaka Chemical in You Only Live Twice (1967).
The film's three leading roles were originally intended for Spencer Tracy, Julie Andrews and Jack Lemmon.