Article 176 of the Family Code
Prior to the amendment of Article 176 of the Family Code of the Philippines (Family Code), illegitimate children were given no right to use the surname of their father.
The only surname they were allowed to use was that of their mother. And this holds true even if their father had expressly acknowledged, admitted, or recognized their filiation.
Back then, the only possible ways for them to legally use the surname of their father were either through adoption or legitimation.
But that had changed with the enactment of Republic Act No. 9255 (RA 9255).
Amending Article 176 of the Family Code, RA 9255 gave illegitimate children the right to use the surname of their father under certain conditions.
Thus, even without resorting to adoption or legitimation, they may now use the surname of their father if the latter had expressly recognized their filiation through the record of birth appearing in the civil register.
The same holds true if their father had admitted their filiation in a public document or in a private handwritten instrument.
Illegitimate children (unless otherwise provided in the Family Code) are those children conceived and born outside a valid marriage.
(References: Articles 165 and 176 of the Family Code of the Philippines and RA 9255)