"Spent the weekend celebrating this amazing guy's mama in his hometown and couldn't be happier #happymothersday," Katie captioned a photo of the cute couple standing outside on a sidewalk.
In the photo, Katie was wearing a black shirt, black jeans and a gray cardigan, while Brandon was wearing a blue striped button down shirt with jeans and a blue baseball hat.
Brandon is an Air Force officer from Chattanooga, TN, who's currently attending Marine Corps University and living in the Washington, D.C. area.
Katie had previously mentioned and shown Brandon in some of her Instagram Stories and Instagram Live postings in recent weeks.
Earlier this month, Katie opened up to fans about her new relationship in an hour-long Instagram Live session in which she revealed details of how she and Brandon first met.
"Brand new boyfriend! Me and Brandon met on Hinge actually, which is a dating app," Katie gushed.
"I was getting really frustrated with dating apps, I'll be honest. I was over it, but after this whole marriage thing happened, I kind of had a different outlook on it."
"I think I felt like I was getting older and I was ready to find something that I wasn't finding," she continued. "But I think this whole experience reminded me of how young I actually am and that I do have time to find that."
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Katie cheated on Derek with her ex-boyfriend two weeks after "Decision Day" filmed last year and then she and Derek called it quits on their marriage on the one-month anniversary of "Decision Day" when they had taken a vacation to Nashville, TN.
Katie and Derek later discussed the demise of their marriage on Married at First Sight's Season 10 reunion special that aired in April on Lifetime.
"I got back on [dating apps]... [and Brandon] asked me out to dinner right before all this quarantine stuff happened, and he ended up picking my favorite restaurant without even knowing it's my favorite restaurant," Katie shared on her Instagram Live.
The new couple's first date presumably took place in mid-March given she and Brandon went out before quarantine regulations were put into place across different states in the U.S. amid the ongoing coronavirus pandemic.
"So we had plans to go there and then he offered to pick me up. I was like, 'Oh, where do you live?'" Katie recalled.
"He gave me a description of where he lives and it turns out it's the same apartment complex that I live in! So I was like, 'Sure, pick me up!' Actually, that wasn't my response. My response was, 'Shut the f-ck up!' And um yeah, excuse my language."
Brandon therefore picked Katie up at her place and she said they ended up having "a great time" together.
"We ended up talking just about the things we want in a relationship for five hours after we had dinner," Katie said.
"So we got to know each other really well, just on the first date. And then all the quarantine stuff happened and we live in the same neighborhood, so we've spent a lot of time together and things are going really well! So, we'll see!"
A fan also asked Katie if Brandon trusts her, and suddenly, he popped his head into the camera and joined her Instagram Live session.
"Sure do!" Brandon interjected.
"I've been pretty straightforward, pretty honest. It's just how I do things," Katie explained.
"He actually knew about the fact that I was on Married at First Sight within, I think, before 15 minutes into our first date. I just wanted to be upfront and make sure he wasn't going to have any big issues with that, and here we are, we're doing good!"
One of Katie's followers asked Brandon to reveal his dreams, which was funny considering Katie was portrayed as being unsupportive and judgmental of Derek's "unrealistic" and "childish" dreams on Married at First Sight.
Katie said she and Brandon were set to have a date night that very night, with Katie gushing, "Brandon brings the fire! Brandon does bring the fire."
Katie has also disclosed on her Instagram Stories she's no longer interested in the ex-boyfriend she had hooked up with while still married to Derek, who also claimed Katie slept with her ex one day after they returned home from their Panama honeymoon while Season 10 was taping.
"The ex is a big ol' BYE... sorry for talking about him so much on the show y'all lol," Katie recently insisted.
Katie also posted a funny photo of Brandon in his military uniform holding up a giant slice of pizza.
On Married at First Sight's reunion special, Katie complained Derek was "fake" and her marriage lacked physical intimacy because Derek allegedly never initiated in the bedroom, but Derek vented about how Katie had allegedly cheated on him twice.