"x x x.
Any person who claims to be a citizen of the Philippines has the burden of proving his or her Philippine citizenship.97 Any person who claims to be qualified to run for the position of President of the Philippines because he or she is, among others, a natural-born Filipino citizen, has the burden of proving he or she is a natural-born Filipino citizen. Any doubt whether or not he or she is natural-born Filipino citizen is resolved against him or her. The constitutional requirement of a natural-born citizen, being an express qualification for election as President, must be complied with strictly. As the Court ruled in Paa v. Chan:98
It is incumbent upon the respondent, who claims Philippine citizenship, to prove to the satisfaction of the court that he is really a Filipino. No presumption can be indulged in favor of the claimant of Philippine citizenship, and any doubt regarding citizenship must be resolved in favor of the State. 99 (Emphasis supplied)
This statement in Paa was reiterated in the 2009 case of Go, Sr. v. Ramos.100 Paa and Go lay down three doctrines: First, a person claiming Philippine citizenship has the burden of proving his claim. Second, there can be no presumption in favor of Philippine citizenship. This negates petitioner's claim to any presumption that she is a natural-born Filipino citizen. Third, any doubt on citizenship is resolved against the person claiming Philippine citizenship. Therefore, a person claiming to be a Filipino citizen, whether natural-born or naturalized, cannot invoke any presumption of citizenship but must establish such citizenship as a matter of fact and not by presumptions, with any doubt resolved against him or her.
x x x."