Although Mindy and Zach ended their marriage weeks before "Decision Day" and Katie was no longer committed to her husband Derek Sherman, Mindy viewed the alleged date as a betrayal since she and Katie had become close friends.
"I will say that Katie did come to me and tell me about it. It still wasn't easy to hear and I don't think it was a very nice thing to do, but I don't know," Mindy told Married at First Sight alums Jamie Otis and Doug Hehner during a recent episode of the couple's Hot Marriage Cool Parents podcast.
Doug recalled how Zach pretended at the reunion he didn't remember how his outing with Katie came about.
"I love how [Zach] was just like, 'I don't know who initiated it,' and then Katie was like, 'No, you messaged me and asked me to get drinks.' It seemed like Zach told you and you were like, 'What the F?!' How were you aware of that? Did that come out from the other cast members?" Doug asked Mindy.
"So Katie messaged me. Actually, I got that message after the first episode premiered, so it was on New Year's Day. And that evening -- it was really late at night -- she felt bad about going out with him," Mindy recalled.
"She messaged me, and it was kind of upsetting. It was just breaking girl code for starters, but also, it's just like everyone's emotions were, you know, super high when the show starts premiering and everything."
It was especially upsetting for Mindy because one of the main reasons she had dumped Zach was because he developed a secretive, inappropriate and disrespectful friendship behind Mindy's back with her close pal Lindsay, who attended theMarried at First Sight couple's wedding.
Zach got caught in a series of lies about his conversations with Lindsay, including what they were about and how often they were had.
"Just to know someone you became close with, I think I was really sensitive to betrayal and everything at that point. So it wasn't easy for me to deal with [Katie and Zach]," Mindy said on the podcast.
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In fact, Mindy was furious when she found out and texted Zach "f-ck you."
Jamie expressed shock over the fact Katie would still go out with Zach knowing he had betrayed Mindy through befriending Lindsay.
Doug pointed out Married at First Sight hadn't aired yet and so Katie didn't see the full extent of Zach's behavior, but Jamie argued Mindy and Katie were friends and so Katie had probably heard plenty of details.
"Didn't she know about everything you had just gone through with another friend and [Zach]?" Jamie asked.
Mindy, however, claimed she was pleased Katie came clean about the "date" right away.
"For me, that's not something that I'm like really holding onto," Mindy concluded.
Katie recently insisted on Instagram her outing with Zach was "not a date."
Katie has also felt the need to defend herself against viewer backlash and Derek's allegations she had cheated on him twice with her ex-boyfriend during their marriage, once right after their honeymoon and then well after "Decision Day," on which Katie had decided to stay married to Derek.
Although Mindy and Zach had a fairytale wedding day, their marriage started going downhill during their honeymoon in Panama, when Zach told his wife multiple times he wasn't attracted to her.
Not only did Zach allegedly avoid spending time with Mindy off-camera, but he even refused to move into an apartment with her following their honeymoon. Mindy then lost all trust in Mindy when the Lindsay situation unfolded.
Following Mindy's unsurprising decision to split from Zach, she threw herself a divorce party and gushed about how she had found an inner strength she never knew existed before.