French singer Romuald (né Romuald Figuier) was a minor star, who took part three times in the Eurovision Song Contest twice representing Monaco and once Luxemburg. He was (and I guess still is) a strong singer, but for some reason if you search for him in the Internet or Spotify, not much information can be found. It seems that he left his marks in some other field than music.
Instead, the composer of the Monegasque entry from 1964 is one of the most succesful (if not the most succesfull) composers ever to take part in Eurovision. Francis Lai is primarily known as a movie composer and his best known score is the music for Love story ("Where do I begin...") which he won a Golden Globe and Oscar for. In Finland his theme for the film Un homme et une femme is often heard in the commercials of a ferry company Silja Line.
Où sont elles passées may not be Francis Lai's best composition, but an ok ballad. In the first part of the 1960's there was no shortage of French ballads in Eurovision, so this song was very much forgotten, even though it came third (out of in the 16 entries).
My points 3/5.