Jon Gosselin alleges ex-wife Kate mentally abused their son, ‘sent him away’ to special needs institution

Jon Gosselin is making bombshell claims against his ex-wife Kate Gosselin after a 10-year gag order has reportedly been lifted.

In an interview with DailyMailTV, the 42-year-old former reality TV star alleged the mother-of-eight mentally abused their 15-year-old son Collin and sent him to a special needs institution in Philadelphia for three years.

Jon says he removed his son from Fairmont Behavioral Health Institute last year after Collin wrote to him, begging for help.

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“Dear Dad, I’m not trying to trick you, but I still love you,” the teen wrote in a June 2017 letter obtained by the outlet. “I told Mom [Kate Gosselin] I want to live with you, she said no. But right? She can’t choose for me. I’m old enough now, I’m YOUR son, not hers. She was abusive to me after I left your house. I’m sorry. Take this to court because … you’re my dad, my savior.”

After receiving the letter, Jon fought for sole custody of Collin as well as 15-year-old daughter Hannah.

Jon alleged that Collin was diagnosed with ADHD and “Kate … couldn’t deal with him."

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“He was alone for three and a half years with no parents, all alone," he further alleged. "It was inhumane."

Jon said, "Other than ADHD, which is extremely common, Collin has never been diagnosed with any known medical condition, there's nothing wrong with him."

Jon claims Collin now suffers from PTSD: "I know my children have suffered abuse and I know one day they're going to tell their own story. And sadly enough, I know what PTSD is. It's really upsetting."

Gosselin also slammed his former spouse over what he claimed are her true motives for continuing to feature on reality TV.

"Kate is not doing the shows for her family, Kate is doing it for herself," he said. "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. She always speaks for the children. It's all lies. They all have voices."

Jon said he believes Kate has "poisoned my children's minds against me."

Pictured: (l-r) Kate Gosselin and John Gosselin talk about their twin daughters and sextuplets on NBC News' "Today" on October 2, 2007

Pictured: (l-r) Kate Gosselin and John Gosselin talk about their twin daughters and sextuplets on NBC News' "Today" on October 2, 2007 (Heidi Gutman/NBC NewsWire)

"It's time America found out the truth about Kate, she isn't the person you think she is," Jon added.

He also tried to clear the air on rumors of infidelity. "I never cheated on my wife, I'm not a monster, I love my children more than anything," he said. "There's a lot of stuff I want to dispel -- there's a lot of untruths."

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Jon said the reason he's speaking out now is because Kate wanted a "gag order" because "she didn't want me speaking the truth."

The Gosselins welcomed twins Madelyn and Cara, 18, in 2000, followed by sextuplets Hannah, Collin, Leah, Aaden, Alexis, Joel and Leah, in 2004.

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The couple split in 2009 after 10 years of marriage.

Reps for Kate did not immediately return Fox News' request for comment.