Brandon Jenner & Kim Kardashian KISSED -- She Smooched Her Step-Brother, BUT...

Kim Kardashian and step-bro Brandon Jenner had an illicit make-out session ... so intimated Brody Jenner, but in reality we've learned there's less here than meets the eye.

Our Kardashian archival sources tell us ... the "kiss" went down when Kim was around 11 and Brandon was 12. Fact is ... Kris and Bruce weren't even married at the time, but they were dating.

The kiss was part of a Truth or Dare game, and it was more like a peck on the lips.

Wow ... Kim learned a lot since she was 11.