Blac Chyna has helped Rob Kardashian come out of his shell very quickly.
In a new Keeping Up With the Kardashians clip, Kim and Khloe Kardashian discuss the big change in their brother now that the 27-year-old model is in his life, noting that the difference is like night and day.
"Don't we kind of think it's a miracle that Rob -- who doesn't even show up to Christmas for the past three years, literally he wouldn't leave his room -- but the fact that now he's created a Snapchat; the fact that he wants to be so public blows my mind," Khloe says.
WATCH: Blac Chyna Celebrates Her Birthday With Rob Kardashian at Chymoji Launch: See Her Baby Bump!
"She gave him confidence, more power to her," Kim replies.
"Even if there's been some drama," Kim adds in a video confessional, addressing all the Chyna-Tyga-Kylie drama that Rob has entered into with his fiancee. "If this is what it takes, then I don't care who he's dating. I'm so happy that he's just feeling better about himself."
WATCH: Tyga Reacts to Ex Blac Chyna and Rob Kardashian's Baby News, Kim Kardashian and Kylie Jenner Also Weigh In!
While applauding Rob's turnaround, however, Kim and Khloe do have harsh words for their brother's openness in discussing his relationship with his family.
"My thing is, do what you want, do what makes you happy. But he should have said to us, 'Hey guys, this is how I feel, I can't help who I love," Kim argues. "Kylie should know this. He just has no loyalty."
WATCH: Tyga Breaks His Silence on Rob Kardashian and Blac Chyna Dating
"Am I happy he's out and about? For sure," Khloe reveals. "Am I disappointed that Rob isn't talking to me after he got out of my house? Yeah."
"I've been the only one that stood by him, and defended him, and wanted the best for him. That's where it gets frustrating," she adds.
WATCH: Why Rob Kardashian Dating Blac Chyna Is So Much More Drama Than You Ever Imagined
Meanwhile, Rob and Chyna are not just engaged, they are also expecting their first child together.
WATCH: Kim Kardashian Hangs Out With Rob and Blac Chyna, Addresses Rumors of Marriage Troubles With Kanye West
The couple stepped out on Tuesday for Chyna's "Chymoji" release party -- the model's emoji keyboard (which may or may not feature her slapping Kylie Jenner) -- where she showed off her burgeoning baby bump.
Watch the video below.
KUWTK airs on Sundays at 9 p.m. ET/PT on E!