Kim Kardashian: Rob Kardashian, Blac Chyna 'not meant to be'

April 21 (UPI) -- Kim Kardashian thinks brother Rob Kardashian and Blac Chyna are "just not meant to be."

The 36-year-old reality star weighs in on Rob and Blac Chyna's volatile relationship in a preview for the April 23 episode of Keeping Up with the Kardashians.

"I've always felt like them as a couple just isn't that healthy, and I think they know that, too. It's not, like, some secret," Kim says in a confessional shot. "Rob can be really irrational and he just has to learn to really take responsibility for himself and not blame it on Chyna. This just has to all stop."

"It's so clear what this relationship is, and they're just not meant to be with each other," she later adds.

The promo shows Kim and mom Kris Jenner's boyfriend, Corey Gamble, visit Rob following his highly-publicized split from Blac Chyna in December. Rob announced Dec. 17 that Blac Chyna left him and took their daughter, Dream.

"I've always been super cool with her. Like, I have a different relationship with her than, you know, what you guys have, and with Kylie [Jenner], and I always hear her out and stuff. Just seeing the motives is what's hurtful," Kim tells her brother in the clip.

Rob and Blac Chyna reconciled in late December, but reportedly ended their engagement again in February. The pair were spotted on a date this week, however, although Blac Chyna wasn't wearing her engagement ring at the time.

"I feel like every person who's in a long-term relationship, or who is committed to their person, goes through ups and downs," the model recently said in the April issue of Cosmopolitan South Africa. "I'm in it for the long haul."

Keeping Up with the Kardashians airs Sundays on E!. The April 23 episode will also show Kris Jenner's heated response to her portrayal in ex-spouse Caitlyn Jenner's memoir, The Secrets of My Life.