Rob Riggle is joining The Masked Singer for the season 5 quarterfinals. The comedian and star sits down on the panel on Wednesday's big episode, and reunites with his former star, Ken Jeong.In ET's exclusive clip from the episode, Jeong is surprised by host Nick Cannon with a piece of fan mail sent in by an audience member.«Dear Ken, I am the world's biggest fan,» Jeong reads aloud from the fan letter.