Gui d'Excideuil ("Guy of Excideuil") is an Old French romance, written in the 12th century, whose text is now lost.
The eponymous hero's lover was a fairy, but he lost her (in an orchard, according to Raimbaut de Vaqueiras) because he began to think about the queen, who loved him unrequitedly.
[1] The story is alluded to by other troubadours such as Peire Vidal in Plus que-l paubres que jatz el ric ostal, and was a well-known story of its time.
[2]