The Most SCARED Sidious Has Been and We've Seen IT!!(CANON) - Star Wars 1

So there is canon evidence that Sidious looked that way already, and the comic seems to imply that this is Sidious’ «true» face that he only shows to Darth Maul. As far as I know, this is all we really have to go on within current canon (aside from the ROTS novelization), since in The Phantom Menace what we see of his Sidious face looks relatively normal.

Por Diego