Amber Portwood's ex- fiancé Gary Shirley dropped a bombshell during season five of MTV's hit reality TV series "Teen Mom OG" when he confronted Portwood with information about her new fiancé Matt Baier's past. Shirley presented Portwood with court documents that allegedly proved that Baier had seven children, when he told her he only had five.

In a series of sneak peeks for part two of MTV's "Teen Mom OG" reunion special, host Dr. Drew Pinsky gives Baier a chance to explain his past and confront Shirley, 29, about his claims, but things get heated when Shirley disrespects Baier, and Portwood, 25, quickly comes to her fiancé's defense.

Pinsky first asks Baier's thoughts on Shirley's reason for bringing up his past. Shirley maintains that he only told Portwood about Baier's alleged seven children because he worried that Baier was lying about other things in his past and he was concerned for his 6-year-old daughter Leah, whom he shares with Portwood. Baier tells Pinsky he thinks Shirley is "full of sh--."

"His motivation for doing what he did was not what he said," the 43-year-old New England native tells Pinsky. "His motivation was different, if he had that motivation, he would've called her and said, 'Hey, what's going on with this?' Instead, he purposely waited for the cameras."

In another clip from tonight's episode, Shirley and his wife Kristina Anderson join Portwood and Baier onstage, and Pinsky gives Shirley the chance to explain his actions, and the men went back and forth about Baier's past, and Baier attempts to squash it and move on from the subject.

"I cleaned up some of this stuff," Baier tells Shirley. "This is actually last season stuff that we're talking about right now."

"And we're dealing with your whole life of trash too, though," Shirley says and starts to list the negative things from Baier's past. Portwood gets visibly upset and she tells Baier, "Don't f--king let him talk to you like that."

"Hold on," Portwood interrupts, raising her finger in the air toward Shirley. "Let me just say something real quick, don't take his kindness right now as a weakness. Do you understand that?"

Watch a sneak peek below, and be sure to catch part two of the "Teen Mom OG" reunion special, airing tonight at 10 p.m. EST on MTV.