Good detective work eru777!
Edit:
Here is a show that Alizée was on with Garou. She sang one of his songs and it was said at some point, he was supposed to either join in or take over, but I think because she was doing such a good job with this song, they let her continue solo.
It's at the 1:30 point where you can see Garou holding the mike up to his mouth and it looks like someone said something to him.