Short answer. Usually not. The Code treats a false reason as simply not written, so the gift stands on its own. It falls only where it appears from the will itself that your father would not have made it had he known the reason was untrue — a narrow exception.
What the law says
The statement of a false cause for the institution of an heir shall be considered as not written, unless it appears from the will that the testator would not have made such institution if he had known the falsity of such cause.
Civil Code, Article 850 — A False Cause for the Institution. Read the full provision →
What the law says
A revocation of a will based on a false cause or an illegal cause is null and void.
Civil Code, Article 833 — Revocation on a False Cause. Read the full provision →
What the law says
The testator cannot deprive his compulsory heirs of their legitime, except in cases expressly specified by law.
Civil Code, Article 904 — The Legitime Cannot Be Taken Away. Read the full provision →
The reason is severed, the gift survives
The statement of a false cause for the institution of an heir shall be considered as not written, unless it appears from the will that the testator would not have made such institution if he had known the falsity of such cause. The default direction matters. The law does not treat an explained gift as conditional on the explanation being accurate; it strikes out the explanation and leaves the disposition standing. Testators give reasons for all sorts of motives — to soften a slight, to justify themselves, to be kind — and the Code declines to let every inaccurate sentence unravel a bequest.
The exception must be visible in the will
The escape route is real but tightly drawn: it must appear from the will. Not from what your father said to relatives, not from what everyone assumed he meant, and not from how plainly false the statement now looks. The will itself has to show that the institution depended on the reason — wording of the order of 'and solely because he did so', or a structure in which the gift is expressly measured by the supposed service. Absent something of that kind in the document, a court is being asked to reconstruct a state of mind the testator did not record, which is precisely what the article's default avoids.
Compare the treatment of a revocation
The contrast with Article 833 is instructive, because it shows the choice was deliberate. There, A revocation of a will based on a false cause or an illegal cause is null and void. — no qualifier, no requirement that anything appear from the will. The Code is markedly more willing to undo a revocation induced by falsity than to undo a gift explained by one. The difference is that a revocation takes something away on the strength of the false belief, while an inaccurate compliment merely accompanies a decision the testator was free to make for no reason at all.
Where the real limit lies
If the objection is that your brother received too much, the productive question is usually not the truth of the stated reason but the legitime. Article 904 provides that The testator cannot deprive his compulsory heirs of their legitime, except in cases expressly specified by law., and it adds that he may not burden or condition it either. Whether the extra share actually trespasses on anyone's legitime depends on the size of the estate, on which compulsory heirs survived, and — where your parents were married — on the property regime being liquidated first. That computation, not the sentence in the will, is what a lawyer will want to run.
Related provisions
- Civil Code, Article 850 — A False Cause for the Institution
- Civil Code, Article 833 — Revocation on a False Cause
- Civil Code, Article 904 — The Legitime Cannot Be Taken Away
- Civil Code, Article 872 — But Never on the Legitime