Short answer. One half of the estate. Under the Civil Code, when legitimate ascendants survive alongside illegitimate children, the children take one half and the ascendants the other half — and the split does not change with the number of grandchildren or the number of ascendants.
What the law says
If legitimate ascendants are left, the illegitimate children shall divide the inheritance with them, taking one-half of the estate, whatever be the number of the ascendants or of the illegitimate children.
Civil Code, Article 991 — Ascendants and Illegitimate Children. Read the full provision →
The halves do not move with the headcount
Article 991 of the Civil Code fixes the proportion before it counts anybody. The illegitimate children take one half whatever be the number of the ascendants or of the illegitimate children. So whether your son left one child or six, that group divides the same half between them, and your half is not reduced. If your son's father is also living, the two of you share the ascendants' half between you. This is the opposite of how most families expect it to work: adding another grandchild dilutes the children's own shares, not yours.
How this article reads today
The share stated in Article 991 was worked out on the classification of children used when the Civil Code took effect in 1950. The Family Code has since changed the underlying rule: the legitime of each illegitimate child is now one half of the legitime of a legitimate child, and except for that modification the Civil Code's provisions on successional rights remain in force. The Family Code also recognises a single class of illegitimate child, so the older Civil Code sub-classifications — the distinctions the 1950 text drew between different kinds of children born outside marriage — no longer apply. Read Article 991 subject to that, and treat all of your son's illegitimate children as one class sharing equally.
Filiation has to be established first
None of this arithmetic starts until each child's relationship to your son is established in the way the law requires — typically by the birth record, by an admission in a public document or a signed private handwritten instrument, or otherwise by the means the Family Code allows. A child who calls your son "papa" but has no recognised filiation is not yet an heir for this purpose, and a child listed on a birth certificate your son signed is. Since your own share depends on how the other half is allocated and not on how many children there are, the filiation question affects them far more than it affects you — but it still has to be settled before any transfer can be registered.
What comes before the division
Article 991 applies to what is left after the estate is cleaned up. If your son was married, the property regime of that marriage must be liquidated first, and a surviving spouse changes the picture entirely; the article as quoted addresses ascendants and illegitimate children only. Debts, funeral and medical expenses and estate tax come off before shares are computed. Where the heirs agree and the children are of age, families commonly settle without going to court; where a minor is among the heirs, expect court involvement. Do not sign a settlement before seeing a full inventory. Nothing here predicts what a particular estate will yield.
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.
- Oceanmarine Resources Corporation vs. Jenny Rose G. Nedic, on behalf of her minor son, G.R. No. 236263, July 19, 2022 — read the decision on LawPhil →