On Monday’s episode of Kate Plus 8, Kate Gosselin opened up about celebrating the sextuplets’ 13th birthday without Collin.

The mom-of-eight treated the birthday kids — Aaden, Alexis, Hannah, Leah and Joel — to a day of camping. The new teens — along with 16-year-old twin sisters Mady and Cara — enjoying a bonfire with s’mores and cake after a fun day of activities.

Unfortunately, Collin — one of the sextuplets — was not at the birthday bash. Last summer, Kate revealed that Collin has “special needs” and is in a program away from home.

“Thirteen — need we say more?” Kate, 42, said to the cameras.

“The photos around the cake, I have them for every year, every child, every birthday,” she shared. “It’s definitely an iconic moment.”

“This year [was] much like last year,” she continued. “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,” she said. “I’ve said that before, I’ll say it again. It’s a bittersweet moment [and] we’ve had many of them.”

“You can’t do anything without realizing he’s missing,” she added. “So we may not say it, but it’s always there.”

Last August, Kate opened up about enrolling Collin in the program away from home.

“This has been a struggle we’ve had for a very long time, and it’s one I’ve dealt with on my own,” she shared. “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.”

Kate said Collin is “enrolled in a program that is helping him learn the skills he needs to be the best him he can be.”

She added: “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.”

Kate Plus 8 airs Mondays (10 p.m. ET) on TLC.