RHOBH 's Kyle Richards and Kathy Hilton's 'Years of Family Trauma' Caused 'Tense Energy' at Reunion

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Kyle Richards and Kathy Hilton's longtime sibling rivalry has come to a head.

A source tells PEOPLE that the sisters and Real Housewives of Beverly Hills costars brought "a lot of tense energy" to the Bravo reality show's soon-to-air season 12 reunion, following Hilton's meltdown during the cast trip to Aspen.

"They cannot reconcile, and it's all so complicated because nobody's backing down. Kyle has backed up her sister for years and no matter what she does, Kathy isn't satisfied," the source adds. "What we're watching is years of family trauma that hasn't been dealt with in a family dynamic."

RELATED: A Complete Timeline of Kyle Richards, Kim Richards and Kathy Hilton's Family Drama

Although the sisters have long had a rocky relationship, the insider says that this moment is "complicated" as it's the "first time" Hilton's two daughters, Paris Hilton and Nicky Hilton Rothschild, have had to intervene.

"They all grew up together. Kyle acted as a spokesperson for the Hilton family for a long time. They always make up, but this is a little different because Kathy is front and center on camera. She hasn't been forced to be vulnerable. Kathy and Kyle have spoken loosely via text only since the reunion," the insider says.

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Although the Aspen drama happened mostly off-screen, Lisa Rinna and her fellow RHOBH cast members recounted Hilton, 63, having a meltdown after the other girls began drinking her competitor's tequila at a bar and wouldn't join her conga line. Rinna, 59, then took Hilton home.

"We get in the sprinter van and Kathy starts screaming about everything, and she'd say things like, 'I'm gonna take down NBC, Bravo, I will take down the show single-handedly. I will f---ing ruin you all!'" she recounted in a recent episode. "What in the holy f---ing hell?"

Rinna continued: "She takes her glasses off, she throws them on the ground, she's jumping up and down, breaking her glasses, she's pounding the walls and she's screaming she 'made' Kyle… Kathy's responsible for Kyle and she said, 'I will destroy Kyle and her family if it's the last thing I ever do.'"

RELATED VIDEO: Kyle Richards Explains Why She May Not Return to RHOBH: 'I Just Want to Live My Life in Peace'

After Rinna and Erika Girardi denied accusations of leaking details from the Aspen trip to the press, Richards, 53, lamented being put in a position of having to choose between her friends and her family.

"I'm not sure what happens from here," she said in a confessional. "If I'm forced to choose between my two friends and my sister, regardless of what happened, it's my blood."

The Real Housewives of Beverly Hills season 12 reunion kicks off Wednesday at 8 p.m. ET on Bravo.