Amber and her beau Matt took a big step in their relationship during tonight's "Teen Mom OG" episode: The Bostonian decided he wanted to spend forever with Leah's mother, and he asked for his ladylove's hand in marriage during a meal at their local diner. After M declared that he'd "really, really like to do something right" and expressed his desire to wed the Indiana native, a visibly shocked A accepted his sweet proposal and a diamond ring. But what was running through her mind during the truly unexpected moment?

"When Matt proposed to me, I was surprised," the 24-year-old explains in the "Teen Mom OG: Featured Moment" below. "I looked at him, and I said 'What?'"

But even though the couple -- who met on Twitter and communicated long distance before Matt relocated to be with his partner -- had openly discussed saying "I do," Amber didn't suspect an engagement was around the corner.

"We had talked about it before, but I didn't think it was something really serious and I didn't think he wanted to that quickly," she continues.

But what was it like to tell her family about her future nuptials? Watch the video to find out, share your well wishes on the engagement in the comments and be sure to keep up with "TMOG" every Monday at 10/9c.