Prem Shastra (1974)

Writer Sagar Sharma is in love with a much younger woman named Barkha. When Sagar meets his ex-wife, Neelima, she tells him that Barkha is her daughter. Perturbed that he is dating his ex-step-daughter, Sagar disbelieves her and continues to have his affair with Barkha. And then Neelima tells him that she had an affair with his elder brother and that Barkha is his daughter. Sagar will now decide to end this affair, as neither the community nor his very own brother will permit him to have an affair with his own niece.