Francis Poulenc only undertook formal musical training with Charles Koechlin in 1921, by which time he had already become identified with Les Six, the six French composers of the circle of Jean Cocteau, including Honegger, Auric and Milhaud. Initially deemed light-weight in style, Poulenc's music acquired a new depth, following the death of a close friend in 1935. At the same time his long collaboration with the singer Pierre Bernac began. Poulenc made a significant and idiomatic contribution to the art of French solo song, in addition to a number of choral works. His solo songs range from settings of Apollinaire and Cocteau to settings of Ronsard.