I'm with GUEST. I watched Andre Rieu last night and saw the same -
the audience knew the words.   I did some checking today.   The song
also was on an older Rieu CD called "Heartstrings", which, for some
reason, could not be ordered by Sam Goody music.    I checked with a
music store specializing in sheet music.   They could not find it,
either.
Are the lyrics Jamas submitted above the same as the audience was
singing?????