"x x x.
Since the court has no jurisdiction over the complaint and respondent, petitioner is not estopped from challenging the trial court's jurisdiction, even at the pre-trial stage of the proceedings. This is so because the issue of jurisdiction may be raised at any stage of the proceedings, even on appeal, and is not lost by waiver or by estoppel.
In Regalado v. Go, the Court held that laches should be clearly present for the Sibonghanoy doctrine to apply, thus:
Laches is defined as the "failure or neglect for an unreasonable and unexplained length of time, to do that which, by exercising due diligence, could or should have been done earlier, it is negligence or omission to assert a right within a reasonable length of time, warranting a presumption that the party entitled to assert it either has abandoned it or declined to assert it.”
The ruling in People v. Regalario that was based on the landmark doctrine enunciated in Tijam v. Sibonghanoy on the matter of jurisdiction by estoppel is the exception rather than the rule. Estoppel by laches may be invoked to bar the issue of lack of jurisdiction only in cases in which the factual milieu is analogous to that in the cited case. In such controversies, laches should have been clearly present; that is, lack of jurisdiction must have been raised so belatedly as to warrant the presumption that the party entitled to assert it had abandoned or declined to assert it.
In Sibonghanoy, the defense of lack of jurisdiction was raised for the first time in a motion to dismiss filed by the Surety almost 15 years after the questioned ruling had been rendered. At several stages of the proceedings, in the court a quo as well as in the Court of Appeals, the Surety invoked the jurisdiction of the said courts to obtain affirmative relief and submitted its case for final adjudication on the merits. It was only when the adverse decision was rendered by the Court of Appeals that it finally woke up to raise the question of jurisdiction.
The factual setting attendant in Sibonghanoy is not similar to that of the present case so as to make it fall under the doctrine of estoppel by laches. Here, the trial court's jurisdiction was questioned by the petitioner during the pre-trial stage of the proceedings, and it cannot be said that considerable length of time had elapsed forlaches to attach.
x x x."