https://lawphil.net/judjuris/juri2003/mar2003/gr_131636_2003.html.
“As to the competency of Elven to testify, we rule that such is not affected by Section 25, Rule 130 of the Rules of Court, otherwise known as the rule on "filial privilege." This rule is not strictly a rule on disqualification because a descendant is not incompetent or disqualified to testify against an ascendant. ( 2 Florenz Regalado, Remedial Law Compendium 583 [7th rev. ed. 1995]) The rule refers to a privilege not to testify, which can be invoked or waived like other privileges. As correctly observed by the lower court, Elven was not compelled to testify against his father; he chose to waive that filial privilege when he voluntarily testified against Artemio. Elven declared that he was testifying as a witness against his father of his own accord and only ‘to tell the truth.’”
“As to the competency of Elven to testify, we rule that such is not affected by Section 25, Rule 130 of the Rules of Court, otherwise known as the rule on "filial privilege." This rule is not strictly a rule on disqualification because a descendant is not incompetent or disqualified to testify against an ascendant. ( 2 Florenz Regalado, Remedial Law Compendium 583 [7th rev. ed. 1995]) The rule refers to a privilege not to testify, which can be invoked or waived like other privileges. As correctly observed by the lower court, Elven was not compelled to testify against his father; he chose to waive that filial privilege when he voluntarily testified against Artemio. Elven declared that he was testifying as a witness against his father of his own accord and only ‘to tell the truth.’”
