The former "Kate Plus 8" star claims their now 15-year-old son, Collin, was "caged" during his 3-year stay at a mental behavioral institution.
Sitting down with DailyMail TV, Jon says, "It's time America found out the truth about Kate, she isn't the person you think she is."
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Speaking openly about the years Collin was sent away, Jon states he wasn't allowed to have contact with his son and alleges he had no idea he was in a treatment facility.
It wasn't until he received a letter from the Pennsylvania Department of Human Services (DHS) regarding an investigation into suspected child abuse involving his son that Jon became aware his child had been removed from Kate's home.
Jon states in his TV interview that Collin was "caged" during his time there and Kate only visited the child three times and less than 2 hours total, all while refusing to disclose where their son was.
Jon claims Collin's roommate smuggled out a letter on his behalf, desperately seeking his dad's help in escaping.
"Please help me and let me meet Colleen [Conrad, Jon’s girlfriend]. I’m counting on you to get me out of here. Daddy, I love you. save me. Please come FAST. I love you. Help me. BYE," the letter reads.
Collin -- who now lives with Jon -- isn't the only child in their family affected by their "militant" mom.
The one-time reality star also claims that Kate alienated and mentally abused their daughter, Hannah, according to the outlet.
"I know my children have suffered abuse and I know one day they're going to tell their own story," Jon says.
"Kate is not doing the shows for her family, Kate is doing it for herself," he insists. "She's narcissistic and selfish. That's it. Period. All of this is for her - 'Kate Plus Eight,' 'Kate Plus Date,' it's her name first."
Jon also calls his ex-wife "delusional" and he can't believe she's fooled everyone into eating up her single-mom act.
"You know, there's stuff that she said in the media that's so far from the truth. It's not even funny. It is the complete opposite of truth," he adds.
Jon states, "The reality is I know how to do math. There's two going to college. There's two that live with me full time and four live with her. So I don't know where eight is coming from."
Jon and Kate divorced in 2009 and share 8 kids together.
They welcomed twin daughters, Madelyn and Cara, in 2000, and Kate followed up with giving birth to sextuplets Hannah, Collin, Leah, Aaden, Alexis, Joel and Leah, four years later.