Zilean knows the origins of Rammus.. and he needs to fess up!

Think about it.. If Zilean is from the Shurima area to begin with, he would be familiar with Rammus origin myths, or at least the idea of Rammus himself. Zilean then travels to every point in time, the beginning and the end, and everything in between, essentially becoming temporally omnipresent.. Zilean has existed in every single point of time.

Zilean must have witnessed how Rammus came to be.