Board Thread:Admin Noticeboard/@comment-4820209-20170816072122/@comment-1584640-20170818095814

http://www.scifijapan.com/articles/2017/08/17/godzilla-planet-of-the-monsters-update/

Apparently according to this new update of the film, this incarnation of Godzilla originated from plant-based life and had super-evolved into the creature he has become. So his origins is an intergration of Biollante's and Shin Godzilla's.