Rob Kardashian and Blac Chyna's relationship getting 'cosy'

Sources close to the unexpected couple tell TMZ, Chyna has been a positive influence on Rob because she's helping him get back in shape.
But don't get it twisted ... we're told they're definitely more than just workout buddies -- the romantic relationship is fairly recent, and things are more playful than serious.

We're told Chyna introduced Rob to her personal trainer about a month ago, and since then they've done several intense workouts together. With and without the trainer, we're guessing.