The family eventually returned to Copenhagen in the early part of the 1960s where she attended a private religious school.
After meeting Richard Dewitte, they soon organized a musical ensemble of five males with Joëlle as lead singer.
Naming the group "Il était une fois" (literally meaning "Once upon a time" in English).
Joëlle Mogensen was also a member of L'équipe à Jojo with Joe Dassin, Carlos, Dave and Jeane Manson.
On May 14, 1982 Joëlle visited her sisters in Neuilly-sur-Seine, Île-de-France, France, then had dinner with friends with whom she spent the night.