"She was pissed," he told ET's Lauren Zima on Wednesday. "And rightfully so."
Harrison said he could tell while speaking with Barb and her husband, Peter Sr., ahead of the show that they weren't in a good mood, but had no idea that Peter's mom was planning to slam Madison so harshly.
Barb said on Tuesday night that she was exhausted after traveling to Australia and waiting to meet Madison. "When she did come in... we didn't get an apology from her, and when I proceeded to ask her if she was madly in love with my son, she said no and she would not accept a proposal in four days," she said. "As a mother, that wasn't what we were expecting."
"When I said I wanted Hannah Ann so badly, it was because... we just clicked right away," Barb explained. "We did not have that connection with Madison."
Madison did not deny Barb's claims, simply offering that she "can't change the past," and Barb doubled down, saying that she, her family and Peter's friends all disapprove of his relationship with Madison. "He's going to have to fail to succeed...Everyone that knows him knows it's not going to work," she hissed.
Harrison said that Barb and Madison did not speak during commercial breaks. "We don't want them to talk, and I don't think Madison was talking anyway," he revealed. "I looked at her, and she was just -- she really got blindsided."
"She was pretty mad about it. She didn't need that or expect it or want that, and I think she -- in her own way -- did the best to kind of diffuse it," Harrison continued. "But she was pretty angry."
Harrison also thought Barb could have been mad at him, or mad at production... or mad at her son, Peter. According to the host, the pilot is equally responsible for making his family wait to meet with Madison in Australia, as the two were talking out their relationship issues as a couple.
"They did wait, and they waited a long time," he said. "It was a conversation... it wasn't makeup. It wasn't that she slept in.... they were having a very serious conversation."
"Madison wasn't throwing a diva fit," Harrison explained. "That wasn't fair. That wasn't just on Madison."
"I would have been dead if looks could kill last night," he joked of Barb's stares. "She was firing."