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Kim Kardashian calls brother Rob a 'lunatic'

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 (Instagram)

Rob Kardashian doesn't appear to be in the best of places in a new preview of "Keeping Up With the Kardashians."

In next Sunday's episode, Kim Kardashian West talks to Scott Disick about Rob's recent questionable behavior, which includes him deleting all of his Instagram pics in July seemingly out of nowhere. Kim then calls Rob's pregnant fiancee, Blac Chyna, to get to the bottom of it, after her brother doesn't pick up his phone.

"I've been trying to get a hold of my brother, and he's totally M.I.A.," Kim says. "Oh, and then he deleted all of his Instagrams, like a lunatic."

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Chyna reveals that she and Rob did indeed get into an argument.

"He does stuff to get a reaction," Chyna says about Rob's social media antics. "He asked me about his business stuff and then I gave him my honest opinion, and then he got upset with me."

"Rob doesn't realize that when he's not in a good mood, it affects everybody, and I just don't want it to transpire to the baby," she adds.

Chyna goes on to speculate that Rob picked a fight with her in order to get out of attending a big family party in San Diego for his grandmother, Mary Jo Campbell, in July.

"I feel like that's what this is all about," Chyna says. "I'll start an argument with Chyna, and I don't really want to go -- it'll give me more of a reason not to go to MJ's party -- and I can blame it on Chyna maybe."

Rob did end up skipping his grandmother's birthday bash, although Chyna was in attendance alongside his sisters, Kim, Kourtney, and Khloe.

Later, Kim gives her two cents on Rob and Chyna's relationship issues.

"I know that Rob and Chyna have, like, an unstable relationship," she tells the cameras. "There's obviously two sides to every story and they just know how to push each other's buttons, and my brother just shuts down and doesn't really tell us because he doesn't want us to turn against him, or against her. So instead, he just comes up with all of these excuses."

"KUWTK" airs Sundays on E!

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