In the book Alex Cross, Alex's wife Maria is shot and killed in Alex's arms at the beginning of the book. She is in early pregnancy at the time. They had 2 children but now have 3 later in the book - how??

In the book Alex Cross, Alex's wife Maria is shot and killed in Alex's arms at the beginning of the book. She is in early pregnancy at the time. At home Alex has a baby girl called Jenelle and an older son called Damon. I was under the assumption that when Maria died her unborn child also died. Yet when the book jumps forward about 10 years it talks about Alex's 3 children, namely a young boy called Ali who seems to be younger than his daughter. So where did this child come from and who does it belong to???