It is settled that by virtue of Presidential Decree No. 892 which took effect on February 16, 1976, the system of registration under the Spanish Mortgage Law was abolished and all holders of Spanish titles or grants should cause their lands covered thereby to be registered under the Land Registration Act within six (6) months from the date of effectivity of the said Decree or until August 16, 1976. Otherwise, non-compliance therewith will result in a re-classification of their lands. Spanish titles can no longer be countenanced as indubitable evidence of land ownership. In the case of Director of Lands v. Heirs of Isabel Tesalona, et al., we took cognizance of this Decree and thus held that caution and care must be exercised in the acceptance and admission of Spanish titles taking into account the numerous fake titles that have been discovered after their supposed reconstitution subsequent to World War II. In both cases, petitioners-heirs did not adduce evidence to show that Titulo de Propriedad 4136 was brought under the operation of P.D. 892 despite their allegation that they did so on August 13, 1976. Time and again we have held that a mere allegation is not evidence and the party who alleges a fact has the burden of proving it. Proof of compliance with P.D. 892 should be the Certificate of Title covering the land registered. Moreover, in the case of Widows & Orphans Association, Inc. v. Court of Appeals, we categorically enunciated that the alleged Spanish title, Titulo de Propriedad No. 4136, had become bereft of any probative value as evidence of land ownership by virtue of P.D. 892 as contained in our Resolution dated February 6, 1985 in a related case entitled Benito and WIDORA v. Ortigas docketed as G.R No. 69343. On March 29, 1985, an entry of final judgment was made respecting G.R No. 69343. Under the doctrine of conclusiveness of judgment, the prior declarations by this Court relating to the issue of the validity of Titulo de Propriedad No. 4136 preclude us from adjudicating otherwise. In the Muoz case, we had cast doubt on the Titulos validity. In the WIDORA case, the Titulos nullification was definitive. In both cases, the Republic and the estate of Mariano San Pedro y Esteban were on opposite ends before this bench. The issue, whether Titulo de Propriedad No. 4136 is valid or not, must now be laid to rest. The Titulo cannot be relied upon by the petitioners-heirs or their privies as evidence of ownership. In the petition for letters of administration the inventory submitted before the probate court consisted solely of lands covered by the Titulo. Hence, there can be no net estate to speak of after the Titulos exclusion from the intestate proceedings of the estate of the late Mariano San Pedro. [G.R. No. 103727. December 18, 1996]