They're two of Married At First Sight's strongest personalities – and when Hayley and Lizzie meet for the first time, things get way out of control. It's one of the show's most shocking fights yet.
"I'm appalled at my behaviour," Lizzie, 28, admits to TV WEEK.
Hayley, who was forced to leave the experiment after her marriage with David turned toxic, returns this week for a girls' night.
Lizzie, who came into this season's relationship experiment late, had already heard a lot about Hayley and what she got up to with Stacey's husband Michael.
"I'd formed a close bond with Stacey and had heard about the cheating," Lizzie explains. "I was going, 'It will be interesting to meet this woman.'"
Lizzie, whose husband Sam cheated on her when she was on MAFS last year, is having a very different experience this year. She's starting to have "incredibly strong feelings" for her new husband, Seb. As she heads out for the girls' night, she's feeling emotional.
"I'm getting scared because of what happened to me last year," she says. "I'm going, 'S--t, I'm really, really, really, really falling for this man.'"
At the girls' night, Hayley starts having a go at Stacey. Lizzie says Hayley's behaviour was "revolting".
"I was very protective of Stacey," she says. "Hayley was pummelling Stacey as a person. You could see Stacey was hurting. I'm there going, 'Hang on – aren't you the one who, while this woman was at home with her kids, decided to hook up with her partner?'"
WATCH: Married At First Sight's Hayley plays Two Minute Speed Date. Story continues below...
However, KC says Stacey was "no saint" herself.
"Some of the things Stacey was throwing out to Hayley were really belittling," she adds. "It [the insults] went both ways."
Eventually, Lizzie had had enough.
"I absolutely lost it," she says.
"I was in such a rage because I couldn't believe someone could be spoken to that way. I was aggressive. I don't condone that."
KC finds herself in the middle of it, as alcohol goes flying.
"Lizzie launched herself at Hayley," she remembers. "I just ran. Cathy grabbed me and pulled me in and I sat on her lap. It was really hectic."
Lizzie felt she couldn't be in the same room as Hayley.
"I told production, 'I'm not going back there while she's there,'" she says. "I'm not proud of my actions. For me to be that way, I was pushed to my limit."