Should a wife be separated from her husband who is ignorant of the rulings of divorce because he is new to Islam, and is his ignorance excused?

If a man divorces his wife with three pronouncements, she becomes irrevocably separated from him and is not lawful for him again until she marries another man—a marriage of genuine desire, not of convenience (tahleel)—and then that man divorces her or dies. Only then is it permissible for her to return to the first husband. The husband's ignorance of the effects of the third divorce pronouncement does not excuse him.