Long known to local Filipino tribes, the 6-foot long lizards are closely related to the world's biggest reptile, the Komodo dragon, National Geographic News reported Wednesday.
The discovery and identification of Varanus bitatawa "comes as an unprecedented surprise," a study published in the journal Biology Letters said, because the lizards' home island of Luzon is "heavily populated and highly deforested."
They probably escaped scientific detection, experts say, because reptile surveys of the mountain forests where they live have been few and far between.
And they are "incredibly secretive," study team member and biologist Daniel Bennett said.
"You could stay in that forest for years and have absolutely no idea that they are there," he said. "They spend all their time high up in trees, more than 20 meters (66 feet) above the ground."
Photographs of local tribal hunters with killed lizards kicked off a two-month search expedition last summer, National Geographic said.