A fisherman in the Philippines discovered what may prove to be the largest natural pearl in existence – but, unaware of the significance of his find, he kept it under his bed for 10 years as a lucky charm.

It would have continued being a hidden secret if not for a fire that ravaged his wooden shack in Puerto Princesa, on Palawan island, the Daily Mail reported.

Weighing 34 kilograms and valued about $US100 million ($131 million), the enormous clam-shaped pearl went on display on August 22 at the Puerto Princesa City Hall after the fisherman showed it to a tourism official.

Aileen Cynthia Maggay-Amurao posted photos of the massive rock online after it passed authenticity checks, appealing for gemologists worldwide to certify its status as the biggest natural pearl ever discovered.