Deux frères (2000)

Paris, 1985. Alain has a great love affair going with his wife Nicole - but also with his mistress Isabelle. When both women get pregnant, Alain decides to privilege his married life and to bring up his legitimate child. As a result, Isabelle gives birth to little Paul anonymously. A few years later the two boys, Martin and Paul, have become friends. But one day, chance has it that Martin learns the truth.