The only way the testator has to exclude a forced heir from the reserved share is by way of («desheredación»)

The disinheritance must be made in the Last Will, expressing the cause it is based on

There are limited legal causes for desheredación for descendants, ascendants and spouse and within them are included those causes of indignity that are applicable respectively to descendants, ascendants or spouse

Apart from what are causes of indignity ( the testator uses one of these causes to exclude a forced heir from the reserved share)
The testator can also use these others:

Related to descendants:

1º) Neglecting to provide the necessary support to live to the ascendant who disinherits when it was needed

2ª) Mistreatment or serious verbal abuse

.
Related to parents and ascendants:

1ª) Having lost Legal authority with respect to the testator due to misconduct in its exercise.

2º) Neglecting to provide the necessary support to live to the ascendant who disinherits, when it was needed ( it is understandable that is once the descendant is of legal age and the Legal Authority finished)

3ª) Attempted murder of one parent by the other, if there was no reconciliation

Related to the spouse:

1ª) Severe and repeated transgression in respect to conjugal rights

2º) Misconduct in the exercise of Legal Authority over descendants

3ª) Neglecting to provide the necessary support to live to their common children or the spouse who disinherits

4ª) Attempted murder without reconciliation.

The cause of «desheredación» must be expressed in the will and therefore the disinherited will be excluded from any share of the deceased’s assets.

If the disinherited forced heir has any children, they will retain the right to the reserved share

The forced heir would need to claim in court for the unfair disinheritance and his right to the reserved share, and then the inheritors would have to prove the validity of the «causa de desheredación»

As the existance of a cause of «indignidad» would not have any effect if the testator had known it at the time of making the will, the existance of a cause the «desheredación», even if expressed in the will, would not have any effect if there is a reconciliation between the testator and the forced heir