The general rule is that, under the first part of Article 904 of the New Civil Code, the testator cannot deprive his compulsory heirs of their legitime or that part of the testator's property which he cannot dispose of because the law has reserved it for the compulsory heirs.
However, the same article provides an exception to the general rule. That is, except in cases expressly specified by law.
Such deprivation of legitime is called disinheritance.
The Supreme Court, in one case, defined it as a testamentary disposition depriving any compulsory heir of his share in the legitime for a cause authorized by law (Remedios Nuguid v Felix Nuguid and Paz Salonga Nuguid, GR L-23445, June 23, 1966, penned by Associate Justice Conrado Sanchez).
A disinheritance, in order to be considered valid, must meet several requirements, to wit: the same must be unconditional, total and made in a will.
Moreover, it must be for a cause specified by law and such cause must be specified in the will. Lastly, the cause must be true and if the truth of the cause is denied, it must be proved by the proponent.
Article 919 of the New Civil Code provides for the sufficient causes for the
disinheritance of children and descendants, legitimate as well as illegitimate:
(1) When a child or descendant has been found guilty of an attempt against the life of the testator, his or her spouse, descendants, or ascendants;
(2) When a child or descendant has accused the testator of a crime for which the law prescribes imprisonment for six years or more, if the accusation has been found groundless;
(3) When a child or descendant has been convicted of adultery or concubinage with the spouse of the testator;
(4) When a child or descendant by fraud, violence, intimidation, or undue influence causes the testator to make a will or to change one already made;
(5) A refusal without justifiable cause to support the parent or ascendant who disinherits such child or descendant;
(6) Maltreatment of the testator by word or deed, by the child or descendant;
(7) When a child or descendant leads a dishonorable or disgraceful life;
(8) Conviction of a crime which carries with it the penalty of civil interdiction.
In essence, if you want to disinherit a child, you must state it in your will and your reason therefor must be a ground provided above. Moreover, the ground you will specify in your will must be real for the same must be proved if the child denies it. Lastly, the disinheritance must comply with other requirements stated above for it to be valid.
Source: Manila Times