Chelsea revealed some "big news" during Part 1 of the Teen Mom 2 reunion: this is her "final season" on the long-running MTV series.

"It is definitely bittersweet," the soon-to-be mom of four told her fellow cast members Briana, Jade, Kailyn and Leah as well as hosts Dr. Drew and Nessa. She first announced this life-changing development on Instagram in November.

Dr. Drew had a "mix of emotions," and he pressed Chelsea to elaborate more on her choice.

"Just watching this last season, I was getting a bad feeling in my stomach," she explained. "It just feels like it's time to close the chapter. I'm almost 30, and I'm having my fourth baby. It just feels like the right time."

How did her cohorts react? Briana stated "more power to you," while Leah wished the DeBoers "nothing but the best."

"I'm really surprised, honestly," Jade said. "I didn't expect it, especially since she's having a new baby and there seemed like a lot of stuff going on. But I totally understand wanting to step back from the reality TV world."

Kail felt the dynamic would change but was looking forward to Chelsea's future.

"I'm really excited to see what opportunities she has once she moves on from this," Kail concluded.

Be sure to watch Part 2 of the Teen Mom 2 reunion next Tuesday at 8/7c.