As soon as the turtle opened his mouth to sing on The Masked Singer Season 3 premiere, fans took to Twitter to insist that he has done this before, in some capacity. Past masked singers have been comedians, athletes, and actors, but some have been singers in real life. And with the turtle, thanks to those singing chops, it seems as though he is a singer outside of the show as well.
Source : https://www.distractify.com/p/who-is-the-turtle-masked-singer