Rob Kardashian Makes Rare TV Appearance to Share Alien Theory

Rob Kardashian broke his elusive tendencies and appeared on his family's show to discuss a matter close to his heart ... conspiracy theories about aliens.

Kris Jenner's only son made a rare appearance on Thursday's episode of "The Kardashians" ... as he joined taping for the show via a phone call to back up sister Khloe's stance on extraterrestrial beings.

Check it out ... the family got on the topic of aliens while discussing the viral Miami moment, where conspiracy theorists claimed aliens visited a mall in the Sunshine state.

Khloe, as well as Kim Kardashian and Kendall Jenner, all vocalized their support for the theory ... though mom Kris Jenner was left unconvinced. Khloe chose to call in some backup ... as she had Rob voice his beliefs for the table -- and the cameras.

He declared ... "There are seven species of aliens and there are good aliens and bad aliens."

Later on in the conversation, Rob shared his theory that aliens have been on planet Earth since at least the 40s. RK found support in Kris' boyfriend, Corey Gamble ... watch the vid, as he declares aliens have been around for centuries.

Corey's passion for aliens left Khloe a little suspicious that CG may be an alien himself ... which Kris quickly shut down in a confessional.

Rob has been popping up on the show more and more lately ... as he recently appeared on "The Kardashians" to have a NSFW conversation about his privates with Khloe.