What is the ruling concerning this child, and is he truly her son, and how can that be, and what is the Shar'i ruling on her situation, and is he a brother to her children from her current husband?

First: Stories like this reinforce confidence in the rulings of Islam that prohibit illicit relations between genders, due to the severe harm they cause to individuals and societies. Moreover, the requirement of the guardian's consent for marriage is a great wisdom for the protection of women and society.

Second: We praise Allah Almighty for your repentance. You should increase your good deeds and charity, for Allah Almighty says: (And indeed, I am the Forgiver of whoever repents and believes and does righteousness and then is guided.)

Third: The marriage of a Muslim woman to a non-Muslim is void. It is not permissible for a Muslim woman to marry a Christian or any non-Muslim. Furthermore, marriage without a guardian and witnesses, with the agreement to conceal it, is void according to the general consensus of scholars.

Fourth: Your son from this Christian is truly your son and is attributed to you. He will be a brother to your children from your mother's side and is not attributed to your current husband. His ruling is the same as his mother's: if she is Muslim, he is Muslim, and what happened from his mother does not harm him.

Fifth: What your current husband did in concealing your matter is praiseworthy. You should hasten to bring your son, raise him, and care for him, and your husband should encourage you in this and complete his kindness.