KJ Apa's alter ego, Mr. Fantasy, just released his first song. (Photo illustration: Yahoo News; photos: iamtherealmrfantasy/TikTok, Stephane Cardinale/Corbis via Getty Images)Who is Mr. Fantasy, and is he actually Riverdale star KJ Apa? That's the question many people have after seeing on their social media feeds a singer in a black wig who bears a striking resemblance to the former Archie Andrews.It all started on Aug. 19, when "Mr. Fantasy" uploaded his first video to TikTok. "Hello TikTok. Hello Los Angeles. Hello world," the performer posted on the video-sharing platform.