Transcript for In 'The Bachelor' finale, Nick Viall finally finds love
As a key player on four seasons of "The bachelor" franchise, Nick Viall has practically made a career out of being single. But tonight that all changed. His transformation from the villain to the sweetheart happening right before our eyes. And here's ABC's Nick watt. Vanessa. Will you -- accept my final rose? Yes. I will. Reporter: Thank goodness. With all my heart. Reporter: Somebody finally fell in love with Nick. Millions of us just watched Vanessa say yes. We just watched sweet raven, heartbroken. Nick cried. If you're a fan, you'll realize that's a theme. Blubbing, sobbing, that was shot in November, we just got a little more up-to-the-minute detail after the final rose. Vanessa is a special Ed teacher. I think she's too good for him. She might be. Look, a lot of us have overkicked our coverage in finding our mate. I think he's a little over his skis with Vanessa. I'm not going to hell Nick I'm falling in love with him. If it doesn't pan out with Vanessa, will you have Nick back? No. Why not? Four times is enough. I think the people of America would just -- that's enough. I was wondering, you know, what you find, you know, so special with Vanessa compared to all the rest of the girls that you're dating right now. He caught a bit of heat from Vanessa's dad. Why wouldn't you? Can I have your daughter's hand in marriage? Are you going to ask the other three girls? Yeah, I am. What dad would not grab their shotgun and run them off the porch? Reporter: Nick had been rejected on national TV twice. On previous seasons -- Kaitlin. Oh my god. Reporter: Andi. I -- I can't go through with what I don't think is right. I'm sorry. Reporter: The fact he came back speaks to the producers. He trusted them to play fair again. Opened himself up again. He was in love with Andi, he was in love with Kaitlin, it didn't end well, those girls ripped his heart out. I have to give him credit. No matter what you say about Nick I give him credit for going there. I'm going to go see Nick and I'm going to have sex with him. Reporter: This season's femme fatal is somewhat sympathetic. My heart is gold but my "Vajine" is platinum. Reporter: This franchise as reality TV juggernaut, arming 7 million plus per episode. For those who aren't fans, one person, a bachelor or bachelorette, is put in a mansion with over 20 potential lifemates and whittles them down to a possible proposal. We started tonight with Vanessa and raven. Nick had to pick. I still can't wrap my head around the concept of the show. He's smooching with multiple women at the same time. I find fascinating about this show the capacity for people to love more than one person at a time. Hi, I'm Chris Harrison. No, I'm not the bachelor. Reporter: Chris Harrison has hosted since season 1. Cheers. Reporter: He thought it might last a couple of seasons. They've now done 21 "Bachelors," 12 "Bachelorettes," two "Bachelor in paradise." From the beginning of the show I didn't have much eppathy or understanding of what was happening. Because I was married. After my divorce is really where I understood why they're here. How difficult it is and how rough it is out there. Reporter: From "The bachelor" to actual weddings, one ongoing engagement from "The bachelorette," three marriages and two current engagement. Babies. We have spawned life out of this show. I mean, think about that. And keep a straight face. I got a note Jaden tanner who I married are officiated their wedding, is are having a baby. Reporter: It's life and love that cannot be produced to ensure a happy ending. There's no million dollars, there's no house at the end of this, there's no car, there's no prize. This is it. Reporter: Season 13, Jason gave Melissa his final rose, then broke it off live on "After the final rose." So mad at you. Reporter: He married Molly, who he had previously dumped on the show. Now they have kids. You follow me? Aah! Oh my god! Reporter: Casting is key. This year the villain -- I love the taste of victory. Reporter: Kind of, was Corinne. I wasn't purposely provocative but I was very flirty and sexy and fun. Perfect. Didn't you show up at the wedding dress thing wearing a bikini? No, that was my costume, that was my outfit. Oh. . The topless in the pool stuff? That was just like, whatever. No. It's a classic piece. It's a classic piece. It's going to be $3,423.20. Thank you. Reporter: We met on Melrose in L.A., Corinne's natural habitat. Were you really falling in love with him? Really? How could you do it with TV cameras around? How does that -- It just happens. I mean, a lot of the people are like, you know -- oh, how can it be real? This and that. It's like, when you're in the situation, you know, it just happens. You like that? Yeah. You really got a genuine problem. We were having a conversation -- I know, I'm sorry. You're ignoring me, looking at clothes. See, this is why my mom hates shopping with me. She'll be talking to me, I'll be like, what did you say? Reporter: Casting, key, remember. Sometimes recurring. You've got a genuine issue. Would you be the bachelorette? I'd love to be the bachelorette. But -- Rachel is going to be amazing. Reporter: Rachel made it to Nick's final four this "Bachelor" season. We chose her because you're invested. If I say Sally from Cincinnati, who is that? I don't know her. Reporter: Rachel will be the first-ever African-American bachelorette. You know, I'm honored to have this opportunity and to represent myself as an African-American woman. What you don't know is the bachelorette starts right now. Reporter: And we just watched "The bachelorette" season basically start. I know that you're going to be meeting a lot of guys. I just want to let you know you don't have to meet any more guys. I'm the guy for you. Reporter: With Rachel meeting some contestants. Now Nick first became a villain in our minds after confronting Andi. If you weren't in love with me -- I'm just not sure why -- like why you made love with me. When we named Nick the bachelor people thought, oh, really, again? Look how beautiful it turned out. Okay what a great story of redemption and love it turned out to be. Reporter: Nick was a little unpredictable. Right now I just feel terrified it's not going to happen. So -- I don't know if I can keep doing this. Reporter: A show in its 21st season needs that. We had a formula. Especially back in the day. That was, you know, one, two, three, steps. Paint by numbers. That's gone. That's long gone now. "The bachelor" has had to evolve and we let people behind the curtain so to speak. You see everything, warts and all. Reporter: It takes a certain type of person to brave this show. Someone sassy like core rain. It's not really me, is it? Nah. No. I think we need a cardigan. Cardigan, anyone? Come on, you're going there already? Reporter: Someone dogged and determined. Like Nick. Vanessa Grimaldi -- will you marry me? Reporter: Now he's engaged. No more bachelor for Nick. Although he is on "Dancing with the stars" next week. The beauty of this show is now you have this man and this woman and they're off television, at least till "Dancing with the stars" starts. But they're off TV and they're going to live their lives, they're going to deal with real issues like does he leave the toilet seat up? Now it's Vanessa and Nick on their own and we'll see how they do. I know them to be in love, I know them to be happy right now. Why not just wish them well? Reporter: Hear, hear. I'm Nick watt for "Nightline" in Los Angeles.
This transcript has been automatically generated and may not be 100% accurate.