It was after they had their first child; roughly two years. At some point, she notices that he suddenly gets increasingly happy and energetic, starts vigorously cleaning beyond his normal habits, and takes a very caring role in the relationship. After a few days, she asks him what's up, and he answers: 'You're pregnant! Of my second child!'
She was on birth control, at the time, but she had it checked and, it turned out, she wás pregnant.
Now here's the nastiness: He should have told her before, because she didn't want another child. She was on birth control for a reason. He clearly did want the child (initially, he didn't, but his hormone rush had pushed him in favour of having this child). There was still some time to get an abortion, but he kind of talked her out of it, and at last she was glad he did, but that doesn't alter the fact that he should have told her immediately... Which he had not, because he was afraid she was going to abort. In any case, had he abstained from telling her to the point where abortion was no longer a legal option, she'd be in her rights to abandon him and the child, and come off without a financial burden for a child she didn't want.