User blog comment:Kogath/Monster Hunter: World Discussion/@comment-6050823-20180401132534/@comment-25119729-20180401133833

"Nergigante was known for a while before the events of MHW"

Let me guess, the guild either wanted to not spread panic by withholding the information or they just forgot about.

Also that tidbit about Xeno, while interesting, also hardens the fact for me that it definetly isn't newborn. While it may not be an adult, it looks more like it used the bioenergy to metamorphose into its current form. Sort of how a freshly hatched butterfly is not a adult, but most certainly not newborn because it already lived quite some time as a caterpillar.