The article presents the diplomatic and interpretative editions of an unpublished and unknown lyric text in Old French, partially notated, whose incipit reads Li rois amur. The study of the Prague manuscript that transmits the lyric allows to trace the copy back to a scholastic milieu of the late 12th-early 13th century. Paleographic and linguistic data converge towards a German-speaking scribe, who seems to have worked on an Eastern French model. The phonetic, morphological and lexical data support the hypothesis of an original text composed in Lorraine or Franche-Comté. The lyric poem, in 3 stanzas of 5 mono-rhymed verses, is of evident courtly inspiration, but differs significantly from the poetic tradition of troubadour ancestry.