Nathan's decision to attack Lowe's character and motives during Hartsock's hometown date impacted The Bachelor star's choice to send Hartsock home during Monday night's episode although Lowe clearly wishes it hadn't.
"I think I would be lying to myself if I said her brother didn't influence me a little bit. Just picturing myself being in their family, I'm not sure I want this guy as my brother-in-law... I don't know if [it was because] the cameras were on or if that's his nature, but ultimately, I chalk it up to him just being a jackass," Lowe told host Chris Harrison during the special's interview-style format.
"But there were other areas in my relationship with Des that were lacking compared to my relationships with the other three women. From our very first date I thought, 'Des might possibly be my wife,' and it almost surprised me when I realized, 'I'm about to send this girl home.'"
Hartsock kept insisting Lowe was making a huge mistake by letting her go, and Lowe said he didn't take her emotional departure very well.
"It crushed me. As she's saying that, I'm thinking, 'Maybe I did. Maybe I did just make a huge mistake and maybe I should turn this around.' But then in the back of my mind I knew, 'Okay if I bring her back in, then one of those other three women have to go and I'm not prepared to make that decision.' I have all the respect for Des in the world and I care for her so much. The last thing I want to do is hurt her, but it was a decision I had to make. Because at the end of the day, I'm trying to find the person who's best suited for me and that person wasn't Des," Lowe explained.
"It killed me and it was a heart-wrenching decision. I just kept asking myself, 'Can I spend the rest of my life with this person?' I not only asked that about Des but I asked that about [Catherine Giudici]. And with Catherine, it was a resounding 'yes.' And with Des, it was an 'I think so.'"
Lowe was completely taken aback by what he had experienced at Hartsock's home with Nathan, as he's extremely offended when someone questions his integrity and honesty.
"Des had told me that her brother had gotten into some trouble as a youth and he's kind of straightened himself out but he's still a little wild at heart. But she definitely didn't prepare me for what transpired. At first I thought, 'Maybe he's joking.' But after about 30 seconds of him ranting, I started to realize, 'Alright. He's not joking,'" Lowe told Harrison.
"I really wanted to hit him. I really did, because I can't think of a bigger insult to hurl towards me because that's not who I am at all. Anyone who knows me knows I'm the furthest thing from a 'playboy.' Attacking my character is the quickest way to get me heated, but I... didn't want to make this a bigger ordeal than it already was, so it took everything in me just to basically control my emotion."
Lowe said Nathan ended up doing a 180 at some point in the night because he had starting things off by complimenting and joking with the Bachelor. Lowe immediately thought they got along nicely and hit it off until things went haywire.
"It was truly one of the strangest turn of events I've ever been involved with," he said.
Another bachelorette whose elimination stood out amongst the rest this season was Sarah Herron. Lowe elaborated on why he felt the need to send her home when he did.
"We had just left the group date cocktail party and Sarah and I had finished our conversation with a kiss. And the kiss, I felt no passion behind it and I knew in that moment, 'This isn't the woman I'm going to marry. I don't have those feelings of love for her,'" Lowe explained.
"And I just couldn't keep her around if I knew that... I was dreading having that [breakup] conversation. I wanted to give her the proper respect and I wanted to be able to explain myself. She ripped out my heart when I watched [her tearful final words]."
Although Lowe went through some difficult moments so far this season, he's grateful his entire The Bachelor journey didn't come crashing down because of Tierra LiCausi.
"It really could have [been ruined]. And that's sad to say, and I'm so thankful that was not the case. When I watch [the season] back I think, 'Man I was such a fool,' because I really do feel like I was duped," Lowe said.
"Oh man, Tierra. You know, my take is Tierra never should have come on the show. She's not suited for this show. She doesn't know how to handle herself in this environment, and I hope she's learned from this, but she's a woman who simply can't get along with her peers. And now that I'm able to watch it back, she's getting into arguments and fights with the sweetest, best people in the house."
Everything that went down with LiCausi apparently left Lowe with one major regret.
"Had I caught wind of everything the girls did earlier, I wouldn't have kept her. You know, in hindsight, I wish I had kept [Jackie Parr] on the two-on-one," he admitted.
In addition, Lowe -- who is reportedly a born-again virgin -- declined to give any details regarding his upcoming fantasy suite dates with AshLee Frazier, Giudici and Lindsay Yenter. He suggested he's just looking forward to getting some private, uninterrupted time with the ladies to talk without cameras documenting their every word.
"I'm excited and I'm also very nervous because I know I'm going to have to make a very difficult decision at the end of this week because I have really started to fall for all three women, and right now, I have no idea who I'm going to send home," Lowe told Harrison.
As far as getting physical inside the fantasy suites, Lowe said, "It's really none of your business."
"A gentleman to the end," Harrison noted at the conclusion of The Bachelor: Sean Tells All.