Rob Kardashian apologizes to sisters for engagement secrecy

Not ready to grovel for forgiveness? Rob Kardashian reluctantly apologizes to sisters Kim, Khloé and Kourtney Kardashian for keeping his engagement a secret from them in Keeping Up With the Kardashians' Sunday, July 3, episode, as seen in a sneak peek.

The E! unscripted series' preview clip shows the ladies sitting down with Rob, 29, about having to find out through social media that he is engaged to girlfriend Blac Chyna after two months of dating. News of the proposal first broke on April 5, when the couple posted pics of the makeup artist, 28, wearing her 7-carat diamond engagement ring.

Kim wants to know if he got down on one knee, and he replies, "I gave her the ring, and then I got on the knee after. It happened spontaneously, so that's why you guys weren't in the loop 'cause I was going to do this regardless — I just didn't know when, and it just ended up happening.

Kim, 35, tells him, "We want to be honest with you — we felt like we should have just at least got a text [that] said, 'Hey, guys. I know you're seeing this on social media. It's true.' People were asking us, and we were like, 'We don't even know if it's true.'"

Rob fires back, explaining that he didn't want to interrupt their vacation in Vail, Colorado, especially since he is under the impression they "hate this girl."

It's a two-way street — you guys could easily have picked up the phone and called me," the Arthur George sock designer says. "No, I'm not going to talk to you guys when you guys are in a room with Tyga and on a ski trip."

Rob ultimately apologizes for the secrecy, and the clip ends with him about to drop a potential bombshell. He tells them he has "one more thing" to talk about, adding that he doesn't want them to get upset about it. Uh-oh — could he be about to reveal that Chyna has a bun in the oven?

A source told Us Weekly exclusively that Rob's mom, Kris Jenner, informed him shortly after the engagement that he was "making a mistake" by moving so fast with Chyna. The model announced in May that she and Rob are expecting their first child together.