Khloé Kardashian and big sister Kim Kardashian are getting on each other’s last nerve these days, as shown in the new Kardashians trailer – and a source exclusively tells In Touch that the bickering and backbiting is getting seriously toxic when the cameras are off.

The Kardashians season 5 trailer was released on May 8 and one of the most shocking moments was the clear tension between Khloé, 39, and Kim, 43. In the clip, Kim called Khloé “judgmental” and said she had a “stick up her ass.” In response, the mom of two commented on the sometimes “vicious” nature between sisters.

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“Kim takes real offense to that and has accused Khloé of being an old lady before her time. She doesn’t understand why she won’t date and instead wants to spend all her time with her kids,” the source explains. “Khloé, meanwhile, throws out jabs about Kim not spending enough time with her kids, which is a very sensitive spot.”

Khloé does “a lot of 𝘤𝘩𝘪𝘭𝘥care” for the SKIMS owner, but the insider says Kim is starting to “resent it” because she “can’t count on her to help out without getting a lecture about her parenting style.”

“But Khloé genuinely feels Kim needs to stop fixating on herself and look after kids a bit more,” the source adds. “After all she’s worth a fortune, it’s not like hurting for money so she can’t say she needs the work.”

Meanwhile, older sister Kourtney Kardashian is “just watching it all” and “relieved it’s not her storyline.”

The source continues, “At the end of the day, while they might ham it up for the cameras, the pain that this sort of nasty behavior causes is very real and very hurtful. It’s now at the point where Kim and Khloé can hardly stand being in the same room, which is pretty sad.”