The pair showed how far they'd come in the BATG journey and left viewers in tears as they convinced their fellow beauties and geeks why they deserved to win.
The first part of the finale, however, had all three remaining couples performing a very steamy Magic Mike dance.
Speaking with Yahoo Lifestyle, Lachy and Kiera said they were not expecting to have to do something so risqué for their final challenge.
"I think you could see the horror in our faces when we were told that's what we were gonna do," Kiera laughed. "Lachlan and I are not dancers and, you know, I think that there's the obvious pressure that Josie is a performer, and even you know George can like street dance and stuff, do backflips!
"Going up against those two guys and Alex and Eliza, who obviously performed really well and their challenges too, it was very overwhelming for me in particular, but Lachlan was amazing and he did put on a brave face. I didn't even realise at the time that you know he wasn't feeling the best either about it."
She continued: "But, you know, it's just daunting in any event, but to go in front of the eliminated contestants and then get told [the dance] will be something that they take into consideration when crowning the winners? It was the most anxious thing I've ever experienced in my life, it really was. It put me completely out of my comfort zone and out of my depth and I felt like a little fish should have in a very very big pond."
Lachy agreed, adding: "I was pretty terrified as well, I have to say. Dancing is not my strong suit. I think it's pretty apparent to anyone who's watching the show, especially the gym challenge and my failed attempts to do star jumps. Hand-eye coordination is probably not one of my strongest assets, so I knew the Magic Mike challenge was going to be a struggle, so thankfully, the whole competition wasn't decided solely on that challenge!"
When asked how their friends and family reacted to the performance, Lachy said they were "completely shocked".
Kiera's friends were equally flabbergasted because they know performing is out of her comfort zone.
"I mean it was crazy and it was obviously very scary, but it's an experience that no one else will ever get to do. So I guess we had to be grateful as well just to be given the opportunity to do it. You probably won't see us on stage of Magic Mike ever again, but that might be a good thing!" she joked.
Most importantly, though, Lachy revealed whether or not he'd had any women sliding into his DM's and the answer is: YES!
"Yes I have, particularly after the makeover episode where I said, 'If the girl of my dreams is out there, slip into my DM's' that triggered quite a big response!" he told us.
However, thanks to Sydney being in lockdown, he has been unable to actually go on any dates, but he did add that he will be keen to get out into the dating scene once lockdown ends.
"When lockdown finally finishes, there'll be lots of girls out there who are going to be desperate to get out and go on dates with anyone, so my theory is that I'll have my pick of the bunch!"
Kiera also added that she hadn't dated anyone since the show wrapped but said the love she's felt from the rest of the cast has "filled that void". However, once she's out of lockdown, she said she'd be "dabbling" in dating.
While there are plenty of reality shows out there where contestants say being on the show has hurt their mental health, Lachy and Kiera say Beauty and the Geek has only positively impacted them.
"I think there are other reality shows, I won't mention any specifics but, you know, a lot of other reality shows get a bad rap and you hear horror stories from contestants who have been on them and had mental health issues afterwards because of what they've been through," Lachy said. "My headspace, my mental health, coming out of Beauty and the Geek is so much far above what was beforehand it's not funny. It has had an unbelievably positive effect on my headspace and mental health and self-confidence.
"Beauty and the Geek, I think, is the only reality show that I ever would have considered going on, and I'm so glad that I did because it is one of the best things I've ever done."
"Couldn't have said it better myself!" Kiera said. "We're so proud of the cast. The show did such a great job of highlighting how much everyone grew and how amazing each member of the cast actually is."
Lachy also added that while social media often gets a bad rap, he's only seen positive comments to come out about the show and he was "overwhelmed" by the fan reaction.
Kiera also noted that host Sophie Monk was incredible to work with, "She was there for everyone and would be so happy to chat with you."
"It's a massive credit to her that we were so comfortable around her as well, and she's gorgeous and not just her looks... she's amazing, and we couldn't have had a better person to host the show!"
Speaking of their huge $100,000 win, Kiera said she'd likely use her half to buy a house at some stage, while Lachy is keen to put his towards his company.
However, he also added that he'd like to dedicate his win to his late grandmother, who passed away at the age of 98 just three weeks after filming finished.
"The fact that she stayed alive long enough that I was able to complete the filming and go and say goodbye to her for the last time was really lovely. I didn't get to tell her that we won, but she'll be watching down wherever she is now, and I know that she'll be really proud of what we've achieved."
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