Le Fils naturel, ou Les épreuves de la vertu (English: The Natural Son) is a 1757 play by Denis Diderot.
Diderot followed the play with a treatise on theatre entitled Entretiens sur le fils naturel; this, and Diderot's other publications on theatre, was largely responsible for the play attaining canonical status.
[1] Diderot modeled Le Fils naturel on Carlo Goldoni's Il vero amico, a comedy about two friends who are in love with the same woman, as well as Pierre Corneille's Don Sanche d'Aragon, which shares with Le Fils naturel a sudden twist in the denouement and a similarly named main character.
It is believed that its first staging was in Saint-Germain-en-Laye, at a residence of the Duc d'Ayen, perhaps for a limited, private audience.
[3] Le Fils naturel tells the story of Dorval, a young man of unknown parentage, who is welcomed into the family of Clairville and his widow sister Constance.