The older brother of Lori Vallow, the so-called "doomsday cult" mom charged in the deaths of her two children and her former husband, grew concerned when she and their other brother adopted apocalyptic beliefs.

Adam Cox discussed his sister in a bonus episode on the podcast "The Followers: Madness of Two," which detailed the tangled case over several episodes. He described her as a great sibling who played sports while growing up in a Mormon family in Southern California. 

Years later, Vallow and her brother, Alex Cox, embraced doomsday prophecies, even before she met her fifth husband, Chad Daybell, an author who wrote about such beliefs. 

REMAINS FOUND ON IDAHO PROPERTY ARE LORI VALLOW'S MISSING CHILDREN, FAMILY SAYS; CHAD DAYBELL CHARGED

Lori Vallow, 46, and her husband, Chad Daybell. (Madison County Sheriff's Office)

"I will say this with Chad Daybell even though I don't know a lot about him," Adam Cox said. "When he met Lori and Alex, they were already — when I say the perfect storm, they were ready to be taken."

"I think maybe Lori had been mentally ill maybe her whole life," he added. 

Vallow and Daybell face conspiracy and murder charges in connection with several deaths, including her two children — Joshua "JJ" Vallow, 7, his 17-year-old sister Tylee Ryan — and 49-year-old Tammy Daybell. 

"Knowing what Lori and Alex were going through with these people that were talking about the end of the world, and knowing how Lori was — and Lori talked about death a lot actually, talked about the next life, how great the next life is and how it's going to be perfect and how her kids won't have to suffer in the next life," Adam Cox said in a bonus podcast episode released Wednesday.

"I thought, 'If they're good, Lori, you tell me where these kids are,'" he added. "If she says, 'Well, I'm not going to tell you where the kids are,' that means the kids aren't alive. I knew right then and there that the kids were dead."

This combination photo of undated file photos shows Joshua Vallow, left, and Tylee Ryan.  (National Center for Missing, Exploited Children via AP, File)

Vallow was arrested in January 2020 in Hawaii after she failed to present the children – who were reported missing months prior — at the request of Idaho child welfare workers. Their remains were discovered on Daybell's property months later.

Daybell is also charged in connection with the death of his former wife, Tammy Daybell, who died a few weeks before he married Vallow. Vallow is also charged in connection with the July 2019 death of her estranged spouse, Charles Vallow. 

He was allegedly shot and killed by Alex Cox, who was never charged and died of natural causes.

Vallow and Daybell have pleaded not guilty to the charges against them. The complex case took a turn after Vallow was declared by a judge to be mentally unfit to stand trial. 

Lori Vallow appears in court in Lihue, Hawaii on Feb. 26, 2020. Her older brother, Adam Cox, appeared on a podcast during which he recalled growing up with his sister and how her behavior changed once she adopted religious and doomsday beliefs.  (AP)

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"My mom and dad have written Lori in prison, and the letters that they've got back from Lori are that Lori has not changed at all her stand or her persona," Adam Cox said. "Apparently she's not talking to anybody. So, at this point, she can't defend herself because she doesn't answer any of the questions that they ask her."

Idaho prosecutors said they intend to seek the death penalty for Daybell.