Preliminaries aside, we now tackle the main issues.
Petitioner refuses to recognize Martin as his own child and denies the genuineness and authenticity of the child’s birth certificate which he purportedly signed as the father. He also claims that the order and resolution of the trial court, as affirmed by the Court of Appeals, effectively converted the complaint for support to a petition for recognition, which is supposedly proscribed by law. According to petitioner, Martin, as an unrecognized child, has no right to ask for support and must first establish his filiation in a separate suit under Article 283 in relation to Article 265 of the Civil Code and Section 1, Rule 105 of the Rules of Court.
The petitioner’s contentions are without merit.
The assailed resolution and order did not convert the action for support into one for recognition but merely allowed the respondents to prove their cause of action against petitioner who had been denying the authenticity of the documentary evidence of acknowledgement. But even if the assailed resolution and order effectively integrated an action to compel recognition with an action for support, such was valid and in accordance with jurisprudence. In Tayag v. Court of Appeals, we allowed the integration of an action to compel recognition with an action to claim one’s inheritance:
…In Paulino, we held that an illegitimate child, to be entitled to support and successional rights from the putative or presumed parent, must prove his filiation to the latter. We also said that it is necessary to allege in the complaint that the putative father had acknowledged and recognized the illegitimate child because such acknowledgment is essential to and is the basis of the right to inherit. There being no allegation of such acknowledgment, the action becomes one to compel recognition which cannot be brought after the death of the putative father. The ratio decidendi in Paulino, therefore, is not the absence of a cause of action for failure of the petitioner to allege the fact of acknowledgment in the complaint, but the prescription of the action.
Applying the foregoing principles to the case at bar, although petitioner contends that the complaint filed by herein private respondent merely alleges that the minor Chad Cuyugan is an illegitimate child of the deceased and is actually a claim for inheritance, from the allegations therein the same may be considered as one to compel recognition. Further, that the two causes of action, one to compel recognition and the other to claim inheritance, may be joined in one complaint is not new in our jurisprudence.
As early as  we had occasion to rule thereon in Briz vs. Briz, et al. (43 Phil. 763 ) wherein we said:
The question whether a person in the position of the present plaintiff can in any event maintain a complex action to compel recognition as a natural child and at the same time to obtain ulterior relief in the character of heir, is one which in the opinion of this court must be answered in the affirmative, provided always that the conditions justifying the joinder of the two distinct causes of action are present in the particular case. In other words, there is no absolute necessity requiring that the action to compel acknowledgment should have been instituted and prosecuted to a successful conclusion prior to the action in which that same plaintiff seeks additional relief in the character of heir. Certainly, there is nothing so peculiar to the action to compel acknowledgment as to require that a rule should be here applied different from that generally applicable in other cases. x x x
The conclusion above stated, though not heretofore explicitly formulated by this court, is undoubtedly to some extent supported by our prior decisions. Thus, we have held in numerous cases, and the doctrine must be considered well settled, that a natural child having a right to compel acknowledgment, but who has not been in fact legally acknowledged, may maintain partition proceedings for the division of the inheritance against his coheirs x x x; and the same person may intervene in proceedings for the distribution of the estate of his deceased natural father, or mother x x x. In neither of these situations has it been thought necessary for the plaintiff to show a prior decree compelling acknowledgment. The obvious reason is that in partition suits and distribution proceedings the other persons who might take by inheritance are before the court; and the declaration of heirship is appropriate to such proceedings. (Underscoring supplied)
Although the instant case deals with support rather than inheritance, as in Tayag, the basis or rationale for integrating them remains the same. Whether or not respondent Martin is entitled to support depends completely on the determination of filiation. A separate action will only result in a multiplicity of suits, given how intimately related the main issues in both cases are. To paraphrase Tayag, the declaration of filiation is entirely appropriate to these proceedings.