Kim, Rob & Blac Chyna: Who's The Third Wheel?

Kim Kardashian is back to hanging out with her baby bro and his fianceé/her former BFF.

Kim was hanging with Rob Kardashian and Blac Chyna Tuesday morning in Bev Hills -- only the second time we've seen Kim and Rob together since before her wedding ... 2 years ago!

We broke the story ... Kim played peacemaker in the family rift over Rob's shotgun engagement by having a sit down with her old pal Chyna.

So who's the third wheel? We'll call it one big happy family. For now.