Karrueche, who was Chris' gf at the time, actually had her arm around Nia in a photo they took -- with Christina Milian too -- during a Las Vegas party back in May 2013. Chris was nearby ... mean-mugging with his homies.
Nia got pregnant with Chris' baby later that summer. We're guessing the ladies won't be having a reunion anytime soon.
We've also learned Nia was very popular on the video vixen scene ... appearing in several music videos, including a half-naked role in Phil Wade's "Dreams of You" video.