Claim: Gemma di Vergy (premiered 26 December 1834) is Italian and based on Charles VII chez ses grands vassaux by Giovanni Emanuele Bidera.
Evidence: It is based on the tragedy Charles VII chez ses grands vassaux (Charles VII and His Chief Vassals) (1831) by Alexandre Dumas père, which was later to become the subject of the opera The Saracen by the Russian composer César Cui. 
Charles VII chez ses grands vassaux by Alexandre Dumas père