The central twist occurs at the very end of the film during the birth of the baby. Throughout the movie, the audience is led to believe the child is Renato's. However, when the baby is born, he is clearly of Asian descent.
This reveals that during the drunken blackout at the wedding, Maru slept with a Chinese guest (seen briefly in flashbacks), not Renato. Despite this revelation, Renato recalls his bond with the unborn child and Maru. He chooses to stay and raise the child as his own, proving his love is unconditional. The film ends with a video Renato makes for his son, jokingly preparing him for the bullying he might face for looking different, affirming they are a family regardless of DNA.