Kris, along with former stepdaughters Kim, Kourtney, and Khloé are claiming Caitlyn lied in her memoir The Secrets of My Life and sources are revealing exclusively to Life & Style that her son Brody Jenner has her back.
"He can't stand that the family is calling her a liar," the source says.
(Photo Credit: Getty Images)
To shoot down the allegations, Caitlyn, 67, wants the family to undergo lie detector tests on live television — and Brody, 33, has been encouraging her to do it.
"Caitlyn and Brody are disgusted with the Kardashians," adds the insider. "They feel Kris and her daughters have done nothing but try to sabotage her."
Last month, Kris, 61, expressed her anger over Caitlyn's book on KUWTK and accused her of trying to make her look bad.
You can watch her reaction in the video below:
She is also plotting her revenge in the form of a memoir of her own, as Life & Style previously reported.
"Kris has been working on a tell-all for years, but now she's fast-tracking it because of the horrible press she's getting," the source said. "Kris can be ruthless when she has to be, and she's going to play as dirty as Caitlyn... Actually, she's going to get even dirtier."
The insider continued, "She wants to name women and men that Caitlyn may have fooled around with. It will shock readers... She'll do whatever it takes to make her book outsell Caitlyn's."
For more exclusive celebrity news, be sure to pick up the latest issue of Life & Style, on newsstands now. For more photos of Caitlyn with her grandkids, check out the gallery below!