Sibling rivalry reached a boiling point on “Keeping Up with the Kardashians”.

During one episode, Kourtney Kardashian, 40, and Kendall Jenner, 23, had a falling out over a ski trip to Mammoth, California that Kourtney took with Kendall’s friends back in January.

Kendall opened up to Khloé Kardashian, 34, about how she felt her older sister had been making jokes at her expense throughout the trip.

“You know, Kourtney and I have been getting a bit closer over the past couple of years and I love that she hangs out with me and my friends,” Kendall said.

“But to be honest, I felt like there were just some moments where she was a bit rude and it really started to get to me at a certain point.”

“A lot of the trip, people were picking on me, and by people I mean Kourtney, most of the time,” Kendall continued.

“Whether she thought she was joking, I didn’t really think it was a joke. I just felt like she was trying to be cool in front of my friends and like, younger people that are cool, at my expense.”

Kourtney, on the other hand, had no idea how her sister felt.

“I thought maybe Kourtney would apologize for the way she was acting on the trip, but it seems to me that she’s pretty oblivious,” Kendall said.

“She has no idea what’s going on. It’s just awkward right now and I’m over it.”

The situation finally came to Kourtney’s attention when Khloé confronted her for “bullying” Kendall and making “digs” at her.

Kourtney insisted that everything was just “jokes” and that Kendall was acting too “uptight” and wouldn’t even let the group stray from their grocery list.

“I definitely think it was unfair for Kendall to say that I was bullying her. We were just having a good time,” Kourtney argued.

“She’s just way more uptight than I thought because I wasn’t trying to make fun of her at all. It’s just my personality to make jokes.”

Khloé didn’t know who to believe. “So I have no idea what trip Kendall and Kourtney were on, but they were not on the same trip,” she said.

“Their stories are so polar opposites. I’m not saying anyone is lying, it’s just they have very different ideas of what happened.”

When Khloé revealed Kourtney’s side of the story to Kendall, it only made her more upset.

“I don’t think she would ever straight up say, ‘Yeah, I do things to Kendall to make myself feel better or make her friends laugh or get validation from other people,’ ” Kendall said.

“But I know everything that I felt is true and real.”

“Your feelings are very valid,” Khloé acknowledged. “Especially when it’s feeling like someone is bullying you.”

“You shouldn’t have to be talked out of that feeling, someone should just stop bullying you.”

Kendall was particularly upset when she found out that Kourtney had claimed she wouldn’t let them stray from their grocery list. “Shut the f— up,” Kendall said.

“I didn’t say anything about steering off of a list. Bible. I did not say one thing about steering off of a f—ing list. I hate that she’s trying to make herself look better to make me look f—ing crazy. … That is the biggest sack of s— ever.”

“We ended up with like, three carts and I was like, ‘Guys, we’re here for two days, we don’t need all this stuff.'”

“But for her to say that I was uptight about a grocery list is just ridiculous and not true at all.”