Juan Marina was the last Spanish Governor of Guam, but not of the Marianas. When the United States took over Guam in June of 1898, they didn't want and they didn't take the rest of the Marianas. Those islands continued to be Spanish possessions until Spain sold them to Germany in 1899. For the first time in modern history, Guam and "the Marianas" became understood as two distinct entities, isolating Guam from its historical, linguistic, racial and cultural brothers to the north.
Marina, however, couldn't go up to Saipan or Rota to continue being governor of what was still the Spanish Marianas. He was taken to Manila, courtesy of the U.S. Navy.
So the Spanish Marianas (and American Guam) continued under local officials, doing the best they could, until a formal governor could be appointed in both places. For the Spanish Marianas, that would be a challenge. How could Spain govern the Marianas after having lost the Philippines? Yet, Spanish they still were, for the moment.
A mestizo Filipino from Macabebe (Pampanga) in the Philippines, Eugenio Blanco y Leison, had fought on the Spanish side and was stranded, with several hundred soldiers under him, in Manila. To flee the victorious Americans, Blanco and his men high-tailed it to the Pacific, where the Carolines and the Northern Marianas were still Spanish. Blanco was made Governor of the Marianas, based in Saipan.
Things weren't so nice for the Saipanese when the Macabebe soldiers and their families moved there. Lacking military housing, the Macabebes moved in with the locals. Food was harder to come by. Anyone who caused the Macabebes problems were dealt with using punches and kicks, even by Blanco himself. The Saipanese were glad when the Germans finally arrived late in 1899 to take over.
But, there we have it. The last Governor of the Spanish Marianas was a Filipino mestizo, Eugenio Blanco y Leison.