This article investigates a corpus of sixteen thirteenth-century motets whose formal structures are rigorously modelled on the AAB formal type of the trouve`re chanson. This corpus bears witness that the first specimens of hybridization between polyphony and the high-style lyric chanson arose as early as the 1240s, well before the emergence of fourteenth-century polyphonic song. The analysis of the make-up of the AAB form of the motets first reveals that its elements completely match those of the pedescum- cauda formal type of trouve`re chansons. The formal impact of song citations within the corpus is then explored, together with the different modalities according to which they are involved in the makeup of the AAB form. Finally, the analysis of the texture of the works brings to light the singularity of their fabric: remodelled by the structures of the trouve`re chanson, it breaks with the traditional format of the motet and turns into the texture of a motet-chanson.