Kate Gosselin’s Sextuplets Become Teens – But Where Is Collin?

Kate Gosselin threw an epic 13th birthday blowout for her sextuplets – but where was troubled son Collin?

RadarOnline.com has learned Collin, who is being treated for “special needs” at a unique facility far from his home, isn’t in any of the promotional photos or videos for Kate’s upcoming tv special celebrating the milestone event.

Gosselin’s six youngest children — Aaden, Alexis, Collin, Hannah, Joel and Leah — turned 13 last month, and their 42-year-old mom treated Collin’s five siblings to a special camping trip.

As RadarOnline.com exclusively reported, the teen has been sent away to live at a behavioral health facility.

“Collin has special needs,” Kate previously told People. “There’s a fairly fluid diagnosis of what those needs are, but he needs to learn certain strategies to help him deal with things. This has been a struggle we’ve had for a very long time, and it’s one I’ve dealt with on my own.”

And as part of his program, the new teenager can’t leave for family events and holidays, like Thanksgiving.

“Collin has serious anger issues,” an insider close to the family told RadarOnline.com. “He frequently lashes out.”

The source claimed much of Collin’s anger stems from his mom and dad, Jon’s, bitter divorce.

“Collin desperately needed a mother and a father,” the source alleged. “Now, he is resentful and blames his mother for everything.”

Collin was missing from his 12th birthday party last year as well.

“He needs to be in an environment to help him learn the skills and gain the insight that he needs to be the best Collin that he can be,” Kate said on his birthday last year. “So, birthday party without Collin - tough for them, tough for mom.”