Short answer. Yes, absolutely void. Article 37 of the Family Code declares incestuous marriages void from the beginning — and it expressly states that this applies whether the relationship between the parties is legitimate or illegitimate. Being born outside of marriage does not make an incestuous union permissible.
What the law says
Marriages between the following are incestuous and void from the beginning, whether relationship between the parties be legitimate or illegitimate
Family Code, Article 37 — Incestuous Marriages. Read the full provision →
What Article 37 provides
Article 37 of the Family Code identifies two categories of incestuous marriages and declares both void from the beginning: marriages between ascendants and descendants of any degree, and marriages between brothers and sisters, whether of the full or half blood. The article is explicit that the legitimate or illegitimate character of the relationship makes no difference. A father and his illegitimate daughter, two half-siblings who share only one parent outside of marriage — these relationships are incestuous under the law regardless of whether they arose from a valid marriage.
Why legitimacy is irrelevant to the prohibition
The Family Code's treatment of incest is based on blood relationship, not on the legal status of the family bond. The prohibition exists because of the genetic, psychological, and social harms that flow from sexual relations between close relatives — none of which are mitigated by the fact that the relationship arose outside of a formal marriage. An illegitimate child is as much the descendant of a parent, and as much the sibling of a sibling, as any legitimate child. Article 37 makes this unambiguous: whether relationship between the parties be legitimate or illegitimate.
Void from the beginning: what this means
A void marriage is not merely voidable — it is treated as if it never existed. It produces no legal effects between the parties as spouses, and no subsequent act can ratify or validate it. Cohabitation for years, the presence of children, or the ignorance of either party about the relationship does not change the legal character of the union. In the Philippines, while there is no marriage to annul, a court declaration of nullity is still the proper way to confirm the void character of the marriage and resolve property and custody issues.
What to do if this situation applies to you
If you have reason to believe that a marriage in your family may be incestuous under Article 37 — whether your own or a family member's — the practical consequences depend on the specific facts. Property acquired during the union, children born of it, and claims to support all need to be addressed through proper legal proceedings. The void nature of the marriage does not automatically resolve those issues; the law has separate rules for property relations in void marriages and for the status of children. Legal advice specific to your circumstances is essential before drawing conclusions about what rights and obligations apply.
Cases citing this provision
These Supreme Court decisions cite the provision above. We list them so you can read them yourself; the summaries of what each decided are not ours to give.
- Republic of the Philippines vs. Marelyn Tanedo Manalo, G.R. No. 221029, April 24, 2018 — read the decision on LawPhil →