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,[2] which had already been adapted in 1945 for the film Les Dames du Bois de Boulogne by Robert Bresson.

[2] 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.

She knows of an unfortunate noblewoman and her illegitimate daughter, Mademoiselle de Joncquières, who survive by entertaining men in a nightclub.

She asks him to forget the past life into which misfortune had led her and to forgive her part in the cruel trick which Madame de La Pommeraye had played.