Imdb info on Jacqueline Fontaine is such a mess, I have no idea where to begin. (Tried to correct it but good luck with that.) There were/are apparently at least two actresses with this name. The one I am familiar with was an American jazz singer who appeared in such Fifties movies as The Country Girl and The Strip. Her credits have been co-mingled with same-named performer(s) who were active in European movies 20-30 years later. Not same person at all.
She was the lone upbeat, fun, and refreshing ray of sunshine in this otherwise gloomy and mostly depressing "smoking good, alcohol bad" film that is nearly completely otherwise devoid of it. Her impromptu duet with Bing in particular was the single most jovial point, and yet ironically it was also one of the most inwardly turbulent moments in the movie for Crosby's character Frank.
I found myself wishing as I watched that Frank would later run into that vivacious energetic blonde singer, but alas it was not to be.
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Gentlemen, you can't fight in here! THIS IS THE WAR ROOM!