Short answer. Yes, but the burden of proof shifts. Where the testator was publicly known to be insane one month or less before making the will, whoever maintains the will's validity must prove it was made during a lucid interval — proving that shifts the outcome back in the will's favor.
What the law says
if the testator, one month, or less, before making his will was publicly known to be insane, the person who maintains the validity of the will must prove that the testator made it during a lucid interval.
Civil Code, Article 800 — Presumption of Sanity. Read the full provision →
The general presumption, and why your grandmother's case is different
The law's default position is that every person is of sound mind, and ordinarily the burden falls on whoever opposes the will to prove the testator was not of sound mind. But your grandmother's situation triggers a specific exception: because she was publicly known to be insane within one month before she made the will, that default flips, and the burden shifts to whoever is defending the will's validity.
A lucid interval, if proven, saves the will
The statute directly answers your question: the person maintaining the will's validity must prove that the testator made the will during a lucid interval — a period of genuine mental clarity despite the surrounding insanity. If that proof is successfully made, the will is not defeated merely because your grandmother was known to be insane shortly before signing; the law expressly contemplates that a lucid interval at the moment of execution can save an otherwise vulnerable will.
What has to actually be shown
The proof required is not simply that your grandmother had good days generally, but that the will was made during a lucid interval — meaning at or around the actual time of execution, she possessed the requisite soundness of mind to understand what she was doing. General public knowledge of her insanity one month before does not, by itself, decide the outcome either way; it only determines who carries the burden of proving what her mental state was specifically when she signed.
This is a shift in burden, not an automatic outcome
It is worth being precise about what this rule does: it does not itself decide whether the will is valid or void. It reassigns who has to prove what. Without the one-month public-insanity fact, an opponent challenging the will would have to prove unsoundness; with that fact present, the burden instead falls on those defending the will to affirmatively establish the lucid interval. Whether that proof actually succeeds is a separate factual question this article does not resolve on its own.
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.
- People of the Philippines vs. Loreto Dagsil y Caritero, G.R. No. 218945, December 13, 2017 — read the decision on LawPhil →
- People of the Philippines vs. Rogelio Toreno, Jr. y Flores, G.R. No. 250332, November 23, 2021 — read the decision on LawPhil →
- People of the Philippines vs. Lito Paña y Inandan, G.R. No. 214444, November 17, 2020 — read the decision on LawPhil →
- People of the Philippines vs. Renato Bacolot y Idlisan, G.R. No. 233193, October 10, 2018 — read the decision on LawPhil →