In this scene from Sunday's episode of Keeping Up With the Kardashians, Khloe and Kim are hanging out when Khloe gets a call from Lamar. Kim does her best to be cordial when Lamar says hi, but it's clear she's seething on the inside.
"I don't know why Khloe and Lamar are talking, but he hurt her so badly," Kim explains. "As a big sister I'm just really protective, and for her just to be flirting with him on the phone makes me, like, sick to my stomach."
However, when Kim calls her sister out, Khloe isn't in the mood to get attacked.
"I'm flirting with him how?" Khloe asks, clearly annoyed. "By answering the phone and saying hello?"
Lamar and Khloe tied the knot in 2009 after dating for several weeks. They stayed together until 2013 when they officially separated. Their divorce was finalized earlier this year, but the two have consistently stayed in contact since splitting.
This continuing relationship has been a source of tension between Kim and Khloe for some time, and may come to a head in this upcoming episode, which airs Sunday, Oct. 4 at 8 p.m. on E!.