I have watched a Hollywood movie where a main lead lady want to be pregnant through sperm donar but movie's hero changed the sperm from his sperm. As the story goes on the child grows and at his birthday party Hero tells the real truth to the lady and told him that he loves him.
But the lady is going to marry another guy soon and she said no but in the ending seen she changes her decision and go back to him.
Do anybody have any guesses ?
Google gives me the nearest result as
The Backup Plan but thats not true.