ET's Lauren Zima sat down with host Chris Harrison at the show's junket in Los Angeles on Thursday, where he shared that fans will see an emotional moment with one contestant, Caelynn, prompting Underwood to divulge something about himself. The host said the exchange holds so much weight that it will "change the course of the entire show."
"She brings out a story, a personal story, that is one of the most emotional, revealing conversations we have ever had on the show. We were all very much taken aback," Harrison said. "So was Colton, and that kind of prompts things in Colton's life."
"I often joke, 'Oh, it is the most dramatic thing ever.' And I don't want to do that, because it does a disservice to what this conversation is about. Kudos to both of them for her speaking about it and Colton receiving it the right way and then having the conversation that he did," he continued. "It was very memorable, and something that is going to change the course of the entire show."
According to Harrison, the conversation between Underwood and Caelynn, a 23-year-old beauty queen, is "unbelievably vulnerable, open and revealing." "Caelynn kind of started it with something she let go, and I think Colton felt comfortable and I think he felt like he owed her certain things in that space because she had just revealed so much personally," he surmised. "It really is a depth and emotion that we have never really faced before."
Harrison praised Underwood for his openness throughout the entire series, including moments when he discussed the reasons behind his virginity.
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"For me as the host, producer, friend, psychologist that I am-- it allowed me in deeper and it allowed me to do my job better and be a better friend," he expressed. "But it's his story to tell and his world to live in, and I wanted to help him. It's my job. And I felt like I couldn't fully help him until he would allow me in, and allow all of us in, and he did."
And Underwood's reveal isn't the only thing that changed the show this season. "[It's] very unconventional," Harrison teased. "That's the reason why I say it's different than Arie [Luyendyk Jr.], and maybe a little better, just because as much as we pushed Colton, he pushed us."
"He's a strong dude, physically and emotionally, and fence jumping aside, there was a lot of times when he pushed back and it made us think and made us adjust course," he added. "The the season took a lot of twists and turns that it's very raw and just open. I don't think it will feel very produced to you."
The Bachelor returns with a three-hour live premiere on Monday, Jan. 7 at 8 p.m. ET/PT on ABC -- join ET's Bachelor Nation Facebook group here.