For several months, Collin Gosselin, one of Kate Gosselin’s sextuplets, has been absent from episodes of TLC’s “Kate Plus 8.” While the matriarch has previously addressed his disappearance from the limelight and her Pennsylvania home, specific details about his diagnosis have never been revealed, until now.

The 13-year-old doesn’t benefit from being filmed for the docuseries and does better with one-on-one care as opposed to living with his seven siblings, reports Hollywoodlife. “Kate doesn’t want Collin on camera very much because all the stimulation can be difficult for him,” an insider told the site. “Kate decided to sent him to a facility because she thought it was best for him.”

The source added that the teen is flourishing in his new environment, stating, “He’s responding very well to one-on-one instruction. He definitely finds it easier to function and cope better without all the chaos that his home life entails.”

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Kate has yet to comment on the latest report, though she did speak out about Collin’s absence during the latest installment of “Kate Plus 8.” Monday’s episode showed her sextuplets, including Alexis, Aaden, Leah, Hannah, Joel, celebrating their 13th birthday with a glamping and survival camping party.

“This year [was] much like last year. Obviously the difference is that Collin wasn’t there,” Kate said during the installment, as reported by In Touch Weekly. “I am comforted with the fact that my kids, all of them, each unique child, is receiving exactly what they need and that hasn’t changed. I’ve said that before, I’ll say it again. It’s a bittersweet moment. We’ve had many of them.”

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Collin Gosselin’s (right) absence from “Kate Plus 8” has some viewers concerned. TLC

Kate first revealed Collin’s issues in August 2016, telling People Magazine that Collin, then 12, needed to be away from her in order to receive treatment. “Collin has special needs. [There’s] a fairly fluid diagnosis of what those needs are, but he needs to learn certain strategies to help him deal with things,” Kate told the magazine.

“This has been a struggle we’ve had for a very long time, and it’s one I’ve dealt with on my own. I’ve felt very alone in this. By the same token, it’s not something that has only impacted me or him – our entire family has been impacted.”

Three months after Collin’s treatment plan was revealed, his fatherJon Gosselin, whom Kate divorced in 2009, came forward. Jon, formerly of “Kate Plus 8” fame, told ET Online that Kate refused to tell him where Collin was. The father of eight, including now 17-year-old twins Mady and Cara, added that he had not seen his son in a year and a half.

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“I have an idea where he is but I don’t really know. Kate says that Collin is in a special school for special needs kids with behavioral problems. That’s what she tells the press. That what she tells the public,” he said. “I ask, but she doesn’t tell me. She doesn’t answer any of my texts unless they pertain to custody.”

While it is unclear what Jon knows of Collin’s issues today, it appears things are on the up-and-up as far as his relationship with his other children. Jon celebrated the sextuplets’ 13th birthday with girlfriend Colleen Conrad in May. With Alexis and Collin absent, Jon, Aaden, Leah, Joel and Hannah rung in the big day with a cookout, playing football and opening presents.