The Second Twin (French: La seconde vérité, Italian: L'amante infedele) is a 1966 French-Italian mystery crime film directed by Christian-Jaque and starring Michèle Mercier, Robert Hossein and Pascale de Boysson. It was adapted from on a novel by Jean Laborde. It was shot partly at the Billancourt Studios in Paris and on location around Dijon. The film's sets were designed by the art director Jacques Douy.
Pierre Montaud, a respected and married lawyer, falls in love with Nathalie Neuville who is works as a hostess in a nightclub in order to fund her medical studies. However, when a former fiancée of hers is murdered, he finds himself under suspicion for the killing.