Short answer. Yes. Article 910 of the Civil Code provides that donations an illegitimate child received during the lifetime of the father or mother are charged to that child's legitime. Under current law, an illegitimate child's legitime is one-half of the legitime of a legitimate child.
What the law says
Donations which an illegitimate child may have received during the lifetime of his father or mother, shall be charged to his legitime.
Civil Code, Article 910 — Donations Charged to the Legitime. Read the full provision →
The rule in Article 910
Article 910 of the Civil Code states: "Donations which an illegitimate child may have received during the lifetime of his father or mother, shall be charged to his legitime." The cash gift your father gave to his illegitimate child is therefore not a windfall on top of that child's inheritance — it counts against what the child is legally entitled to receive from the estate. When the estate is settled, the value of the donation is deducted from the child's legitime, and only any remaining balance is paid from the estate.
The current size of the illegitimate child's legitime
Article 910 was written when the Civil Code classified illegitimate children differently. The current rule on the share is set by the Family Code, which provides that the legitime of each illegitimate child is one-half of the legitime of a legitimate child, and that except for this modification, all other Civil Code provisions governing successional rights remain in force. The Family Code also recognizes only a single class of illegitimate child — the older sub-classifications in the Civil Code no longer apply. Read Article 910's mechanics against this updated share.
What happens if donations exceed the legitime
Article 910 adds a second rule: "Should they exceed the portion that can be freely disposed of, they shall be reduced in the manner prescribed by this Code." If the cash gifts the father gave during his lifetime exceed both the illegitimate child's legitime and the freely disposable portion of the estate, the excess is subject to reduction. This protects the legitimes of the other compulsory heirs — particularly any legitimate children, whose reserved shares cannot be depleted by excess gifts to an illegitimate child.
Why this matters at estate settlement
In estates where there are both legitimate and illegitimate children, accounting for the donations received by the illegitimate child is a necessary step in computing everyone's shares correctly. An illegitimate child who received substantial gifts during the father's life may receive little or nothing from the actual estate — the gifts have already consumed the reserved share. The legitimate children's shares are computed independently and may not be reduced by donations to the illegitimate child unless those donations exceeded the free portion. Sorting this out requires computing the full notional estate, including all donations subject to collation.