Upon returning from their Vail ski trip, the Kardashian sisters were greeted by their brother who finally comes clean about his engagement to Blac Chyna

Rob Kardashian is just full of secrets!

In a sneak peek at Sundays episode of Keeping up With the Kardashians, Rob finally comes clean with his older sisters about his surprise engagement to Blac Chyna.

“You obviously know what happened based on … social media,” he begins. “But everything that happened, I’m very happy about.”

“So, did you like get on one knee?” Kim asks.

“I gave her the ring and then I got on the knee after,” he responds. “It happened spontaneously, so that’s why you guys weren’t in the loop. I was going to do this regardless, I just didn’t know when … it just ended up happening.”

Kim continues to speak for her sisters and tells Rob that they felt hurt that they didn’t get a heads up, because people were asking them if it were true, but they didn’t even know if was or not.

“If you guys were really concerned and wanted to know, you guys would have said ‘Is this true? Congratulations you just got engaged,’ ” Rob, 29, says in his defense. “Obviously do you think I am just going to post some fake s— because I’m a media w—-?”

Khloé, 32, finally speaks up and flat out asks Rob, “Why would I say congratulations if I don’t even know if it’s true or not?”

“Why would I joke with that?” Rob says. “It’s a two-way street … No, I’m not going to talk to you guys on the phone when you’re in a room with Tyga and on a ski trip … I’m not going to call you guys and say this and that when you hate this girl.”

“But we love you,” Kim, 35, interjects.

“And that’s great, but she makes me happy,” he responds. “She loves me and I’m happy. That’s it.”

RELATED VIDEO: Rob Kardashian and Blac Chyna Make First Appearance Since Announcing Baby News

The three girls continue to state their case all the while telling him that they are happy for him, but they’re also hurt by having to find out via social media. Before the clip ends, Rob hits them with another thing.

“I get I upset you guys. I get that I’m your brother,” he says. “I’m your only brother and I know you’d like to know when something this important happens … and then there’s one more thing I have to talk to you guys about.”

Could this be the scene where he spills the pregnancy news to his sisters?

Since filming, the family has banded together in welcoming Blac into their inner circle. On Monday, the family was all in attendance for Khloé’s birthday bash at Dave & Buster’s in Hollywood, California, including Rob and his wife-to-be.

Keeping Up with the Kardashians airs Sundays (9 p.m. ET) on E!