"Le Chef-d'oeuvre inconnu" (English: "The Unknown Masterpiece") is a short story by Honore de Balzac. It was first published in the newspaper L'Artiste with the title "Maitre Frenhofer" (English: "Master Frenhofer") in August 1831. It appeared again later in the same year under the title "Catherine Lescault, conte fantastique". It was published in Balzac's Etudes philosophiques in 1837 and was integrated into La Comedie humaine in 1846. The work is separated into two chapters: "Gillette" and "Catherine Lescault".

"Le Chef-d'oeuvre inconnu" is a reflection on art, and has had an important influence on modernist artists.

Unlike most other stories in La Comedie humaine, this is set in the 17th century, in the year 1612. Of the three artists depicted in this story, Poussin and Porbus were real artists of the 17th century. Frenhofer is a purely fictional character. In the case of Porbus, Balzac used the gallicized version of the surname of Frans Pourbus.

Paul Cezanne strongly identified with Frenhofer, once saying "Frenhofer, c'est moi" (I am Frenhofer). Critic Jon Kear argues that Cezanne's own attempts to paint the nude were heavily influenced by Balzac's portrayal of Frenhofer's work.

In 1927, Ambroise Vollard asked Picasso to illustrate "Le Chef-d'oeuvre inconnu". Picasso was fascinated by the text and identified with Frenhofer so much that he moved to the rue des Grands-Augustins in Paris where Balzac located Porbus' studio. There he painted his own masterpiece, Guernica. Picasso lived here during World War II.

Sidney Peterson's 1949 avant-garde film Mr Frenhofer and the Minotaur was based on the link between the short story and the work of Picasso. It draws on Picasso's Minotauromachy, bringing Picasso's work to life with the characters of Gillette, Poussin and Porbus participating.

"Le Chef-d'oeuvre inconnu" inspired the film La Belle Noiseuse by Jacques Rivette (1991). (wikipedia.org)