"No one knows where he is. I don't even know. I have an idea where he is, but I don't really know where he is," Jon said. "Kate says Collin is in a special school for special needs kids with behavioral problems."
"I ask but she doesn't tell me. She doesn't answer any of my texts unless they pertain to custody," he added.
"I think it's about money. I think it's about filming and money. That if I get any rights, I'm not going to sign for my kids to film."
Jon and Kate share eight children, 16-year-old twins Cara and Mady and 12-year-old sextuplets Collin, Aaden, Alexis, Hannah, Joel and Leah.
Kate said in the Sept. 5 issue of People that Collin has "special needs" and is enrolled in a program away from home.
"[He] needs to learn certain strategies to help him deal with things," she said. "[The program is teaching him] the skills he needs to be the best him he can be."
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"We miss him so much, so it's been hard because there is this huge hole in our family without him here," she added. "But it comforts us to know he's where he needs to be right now, and I can feel good about that."
Jon told "ET" that Collin's siblings also don't know where he is, and that law enforcement officials have said the 12-year-old isn't at a special school.
The dad has previously claimed that Kate keeps him from their children.
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