"The Unknown Masterpiece" by Honoré de Balzac is a short story first published in 1831. Set in seventeenth-century Paris, it follows three painters: the young unknown Nicolas Poussin, the established Porbus, and the enigmatic master Frenhofer. For ten years, Frenhofer has labored obsessively on a secret painting he believes will be his greatest triumph. When Poussin offers his beautiful lover as a model, the completion draws near—but what will the finished work reveal? A profound meditation on artistic perfection and obsession.
Wikipedia page about this book: en.wikipedia.org/wiki/Le_Chef-d%27%C5%93uvre_inconnu