Taemin is actually a girl. A male trainee who got into SM by Heechul screwed up with his double eyelid surgery, so Taemin cross-dressed and debuted as Shinee.
Taemin was too pretty when he debuted so Taemin himself had to clarify these rumors. When Shinee debuted in Japan, these rumors again surfaced in Japan. EXO Kai was accused to be Taemin's twin when his teaser was released. Rumors said people caught Taemin calling Kai "oppa" and Jonghyun knew his real gender