Short answer. Only the gift to that witness — and to the witness's spouse, parent, or child — is void. The rest of the will stands. The witness is still treated as a competent witness, and the remaining bequests to other beneficiaries are unaffected, unless there are fewer than three other competent witnesses.
What the law says
such devise or legacy shall, so far only as concerns such person, or spouse, or parent, or child of such person, or any one claiming under such person or spouse, or parent, or child, be void, unless there are three other competent witnesses to such will
Civil Code, Article 823 — A Gift to a Witness Is Void. Read the full provision →
The will itself is not void
The Civil Code draws a precise line: when a witness to a will is also named as a beneficiary, only the gift to that witness is voided — not the will as a whole. The rest of the will remains fully effective. This rule reflects the legislature's intent to prevent witnesses from having a personal stake in the will's contents, without punishing other beneficiaries for a situation they did not create and cannot control.
Who exactly loses the gift
Article 823 reaches beyond the witness personally. The void devise or legacy covers the witness, the witness's spouse, the witness's parent, and the witness's child, as well as anyone else claiming through any of those persons. So if the will leaves land to the witness and, upon the witness's death, to the witness's children, the entire chain of that inheritance is affected. The intent is to remove all financial incentive that could compromise a witness's neutrality at attestation.
The safety valve: three other competent witnesses
There is one exception to the voiding rule. If, apart from the interested witness, there are three other competent witnesses to the will, then even the gift to the interested witness and the witness's relatives is saved. When four or more competent witnesses signed, the interested witness's testimony is not needed to establish the will's validity, so the concern about bias disappears and the gift is allowed to stand.
The witness may still testify
A practical consequence of Article 823 is that losing a bequest does not disqualify the witness from participating in probate. The Code expressly states that the interested witness shall be admitted as a witness as if such devise or legacy had not been made or given. For purposes of proving the will, the witness is treated as a competent, disinterested attesting witness. This matters when the will needs to be probated and witness testimony is required to establish its due execution.
What to do next
Whether this situation applies to your father's will depends on exactly how many witnesses signed and who they are. Count the attesting witnesses and check whether any of them — or their spouses, parents, or children — appear in the will as beneficiaries. If only one witness has a bequest and the remaining witnesses are disinterested, the will can proceed to probate intact, with only that one gift excised. If multiple witnesses are beneficiaries, each gift is separately affected. A lawyer reviewing the original will and attestation clause can give you a clearer picture of the estate's situation.