Amber, Catelynn and Maci have known each other for nearly a decade -- and now the Teen Mom OG trio is welcoming two fellow young moms to their unique televised world.

"Hi!" Amber, Cate and Maci all say together as Bristol and Cheyenne walk into the room (as seen in the video above). Hugs ensue, and the reception from the veterans is warm. Then the women sit down and officially kick-start their journey together.

"How does it feel being a part of this show now?" Amber asks the duo.

"[It's] nerve wrecking coming on this show when people have done it for so long," Cheyenne replies.

And how does Bristol respond? And what hopes do the OG girls have for the future with their fellow cast members? Watch the video to find out -- plus their celebratory toast as a brand-new cast. Catch the season premiere featuring the five young women on Monday at 9/8c!