The phenomenon of the imaginary companion is well described among children and elderly people, but is rarely evoked in adolescents. Its manifestation at the age of adolescence is often misinterpreted as delirium and a sign of beginning schizophrenia. In this article we present the case of Julie, a seventeen-year-old teenager, in order to illustrate the hypothesis that the imaginary companion can appear within other psychopathologies than those of psychosis and schizophrenia. The young woman uses an imaginary companion she calls « Monseigneur » (« Mylord ») to compensate for an underlying depression. We describe in detail this clinical situation, the different stages of the therapeutic treatment and the psychological evolution of Julie.