How Khloe Kardashian's Sisters First Reacted to Tristan Thompson's Cheating Scandal -- and Who Told Khloe

The NBA pro allegedly cheated on the reality star right before the birth of their daughter, True.

Khloe Kardashian’s sisters are about to learn about Tristan Thompson’s cheating scandal. 

In an E! News sneak peek of Sunday’s all-new Keeping Up With the Kardashians, Khloe's sisters first find out online that Tristan was allegedly spotted making out with another girl just before the couple’s now 6-month-old daughter, True, was born. 

In the clip, Kendall Jenner, Scott Disick, Kim Kardashian West, Kourtney Kardashian and Kylie Jenner all react to the report that the NBA pro was unfaithful to Khloe. 

Kendall is in the car with Scott when she gasps aloud at a text she’s receives from Kim. “Stop! Bro, that’s pretty serious, isn’t it,” Scott exclaims, before questioning if it’s “for sure, for sure.”

“I don’t know, that’s what I’m trying to find out,” Kendall responds.

Later, Kendall goes on to read out loud some of the source reporting about the incident. “The woman who filmed the clip said, ‘I was there and he was on the table right next to us with a group of friends. Everybody watched them make out several times,’” she reads.

“I’m, like, in shock right now. I don’t even know what to say,” Kendall says. “What a f**cking idiot. It’s a sick joke… Oh my God, I’m going to cry for her.”

Meanwhile, Kim was on set filming for the show when she learned the news. In the clip, she stares intently at her phone and asks everyone to hold on, before saying, “Yikes.”

"There’s video of Tristan making out with a girl last night,” Kim reveals to the cameras. “Khloe’s going to die.”

Kourtney appears to be walking through her house as she digests the information. “I mean, I can’t even imagine being in Khloe’s shoes,” she says in the confessional. “Just how reckless it all seems. This is really shocking and obviously heartbreaking. The whole thing makes me disgusted.”

The sisters quickly learn that their youngest member, Kylie, sent the article to Khloe.

“Like do I call Khloe?” Kim questions to herself. “... She’s literally going to go in labor over this.”

“Oh no,” Kendall tells Scott. “She def knows, but she’s not responding to the texts.”

For Kylie, it was important to tell Khloe herself, so she wouldn’t find out online.

“No one had the courage to tell Khloe because we knew she was days away from giving birth, we didn’t want to stress her out, but we knew it was the right thing to do,” Kylie, who was getting her makeup done when she learned the news, says in the confessional. “So, I’m the one who told Khloe. I didn’t want to hurt her feelings, but I felt like she should hear from one of us versus on the internet.”

The new clip comes a few days after a source told ET that Khloe flew back to Cleveland, Ohio, with Tristan -- where he plays for the Cleveland Cavaliers -- after initially putting her move on hold.   

"Khloe and Tristan are still working on things, but know whatever they decide to do moving forward, it will be whatever is best for their daughter, True," the source said. "Khloe isn’t certain how long she will be in Cleveland and may fly back for her mom, Kris [Jenner's], birthday next week, but isn’t sure. A lot is dependent on how things go with her and Tristan.”

While in Cleveland, Khloe sat courtside at Tristan’s game.  

The move comes as a bit of a surprise. Last month, a source told ET that Khloe was unsure if she was going to return to Cleveland, largely in part because it’s “been hard” for her to relive the scandal while watching this season of KUWTK

"As much as she's worked on moving past the heartbreak, the reminder brings up some of those emotions again," the source said. "Khloe will most likely head back to Cleveland, but as of now, there isn't an official date."

Despite the uncertainty currently in their relationship, Khloe and Tristan did spend Halloween together with True, who they dressed as a flamingo.  

Keeping Up With the Kardashian airs Sundays at 9 p.m. on E! Watch the video below for more on Khloe and Tristan: