The 23-year-old builder was confronted by Ali after Charlie told her he had been discussing rumours about her relationship with Bachelor In Paradise star, Grant Kemp.
"We were all sitting around the pool and the topic of the rumours was brought up," Nathan told Now To Love. "A few of the boys had said what they had heard and I basically just said what I had heard."
“I'm pretty well networked in the reality TV show circuit," he said. "You meet one person and the next person and the next person and so I know a few of her [Ali] friends."
"It wasn't like I sat down with anyone and they said, 'this is what happened - this is who Ali is' or anything like that, it was just I heard bits and pieces and a story would come out and then someone would say 'that's true' and I just had my judgement of the whole thing."
During the heated confrontation, Nathan hit back at Charlie, calling him jealous and malicious.
"I really, really feel sorry for Ali if she ever, ever ends up with you. You're a f---ing spiteful and jealous person," Nathan fired at Charlie. "110 percent and I'll take that to my grave. You're a spiteful piece of sh-t."
While he says he doesn’t hold grudges, he does describe the 31-year-old as selfish.
"We're two completely different people. I am very selfless and to me, he is very selfish. Everything has to benefit him."