This is just heartbreaking. On last night’s episode of Kate Plus 8, Kate Gosselin was feeling a whole range of emotions as she and her brood celebrated the thirteenth birthdays of her sextuplets — though her son Collin was noticeably absent from the mix. For more than a year, Collin has been away from his siblings — 16-year-old twins Mady and Cara and fellow 13-year-old sextuplets Aaden, Alexis, Hannah, Joel, and Leah — as he’s gotten treatment for “special needs.” Learn more about his special needs in the video below.

The reality TV mom, 42, called the decision to celebrate without Collin “bittersweet.” She explained, “Thirteen — need we say more? The photos around the cake, I have them for every year, every child, every birthday. It’s definitely an iconic moment. This year [was] much like last year. Obviously the difference is that Collin wasn’t there. 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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Last year, Kate explained that the decision to send Collin to a boarding school-like program wasn’t an easy but, she felt, a necessary one. She explained at the time, “We miss him so much, so it’s been hard because there is a huge hole in our family without him here. But it comforts us to know he’s where he needs to be right now and I can feel good about that.”

Collin’s father, Kate’s ex-husband Jon Gosselin, has been vocal about how he hasn’t been kept in the loop regarding his son’s education and care. He explained back in November, “I have an idea of where he is, but I don’t know exactly where he is… I mean, I ask but she doesn’t tell me. She doesn’t answer any of my texts.”

Hopefully, all six of the sextuplets will be reunited by the time their fourteenth birthday rolls around next May!