Lady J (French: Mademoiselle de Joncquières) is a 2018 French period drama film directed by Emmanuel Mouret and inspired by a story in Denis Diderot's novel Jacques the Fatalist, which had already been adapted in 1945 for the film Les Dames du Bois de Boulogne by Robert Bresson. Set in France before 1789, it stars Cécile de France as Madame de La Pommeraye, an attractive widow whose bachelor lover, the Marquis des Arcis (Édouard Baer), will not propose to her and gets her revenge by tricking him into marrying Mademoiselle de Joncquières (Alice Isaaz), a former prostitute.

Plot

Madame de La Pommeraye, a young and pretty widow who boasts that she has never been in love, ends up yielding to the advances of the Marquis des Arcis, a well-known libertine, who is diligently and obsessively courting her. When after two years the Marquis begins to neglect Madame de La Pommeraye, she suggests to him that their feeling for each other has faded. He, instead of denying this, agrees wholeheartedly. Deeply hurt by his rejection, she plots revenge.