After both enjoying intimacy week, the couple found themselves in uncharted territory after Cathy became jealous when Josh spoke to another bride during the latest dinner party.
"It was extremely bitter and very toxic," Cathy shared of their first big row.
"The fight happened because I was jealous; I was feeling intimidated because he was speaking to Hayley [Vernon] and I was trying to look for warning signs, if could there be any signs of romance sparking with him and Hayley or him and… anyone he was talking to."
Opening up to Josh about her feelings when they got home, logistics investigator Cathy says she was faced with 'defence' and 'anger'.
"Josh said to me, 'If you have trust issues with me, I will write leave [at the commitment ceremony] because I cannot be with a girl who has trust issues,'" she revealed.
"And it broke my heart that he did that, because it seems like he would be just willing to walk away from this when we haven’t even really started."
The fight took the usually loved-up pair by surprise, Cathy's implied lack of trust in industrial operator Josh had him shaken up.
"I don’t think Hayley crossed a line," he explained in a piece to camera.
"I said there’s nothing to worry about, but she still had the s--ts, so I thought, 'Well, don’t you trust me?' And then it was all about, 'Why don’t you trust me? I’ve never done anything wrong to you.'
"It’s definitely a bit of a worry in the back of my head now. A few red flags for me," he continued.
"If you don’t trust me, what are you doing with me?"
For Cathy, Josh's apparent willingness to walk away was heartbreaking.
"It actually broke me. It hurt so much," she shared.
But trust issues could truly be a dealbreaker for Josh:
"If the trust isn’t there, unfortunately, the relationship’s not there, for me."
Cathy and Josh started out stronger than perhaps any other couple – making this tiff all the more shocking. Both of them each secretly admitted during their reception that the other could be 'The One', only a few hours after marrying, and they've gone from strength to strength ever since.
"Aww, strewth!" Josh exclaimed appreciatively when he first saw his bride on their wedding day.
"Here she is. Hooley dooley. She's gorgeous!"
Cathy felt the same way.
"He had this massive grin and his eyes were just so... blue," she gushed after meeting her husband.
"I dreamed of a man with light hair, light eyes, tanned skin, nice smile – and here he is."