Reporter: The bride to be. I'll have a p'nina tornai dress. And a crystal tierra. Reporter: She's queen of the wedding castle. We'll have pastel flowers, and a vanilla bean cake with white fondant.... See More
Reporter: The bride to be. I'll have a p'nina tornai dress. And a crystal tierra. Reporter: She's queen of the wedding castle. We'll have pastel flowers, and a vanilla bean cake with white fondant. Vanilla? Not on my watch. We're having chocolate. Reporter: But what if the king comes in and takes the cake? These days, more and more grooms are crashing the party planning. My baby looks beautiful. Reporter: Some even featured on the show "Say 'yes' to the dress". It's awful. It doesn't flatter her body at all. Reporter: We're at Kleinfeld bridal in New York City where every year over 17,000 brides rendezvous with the dress of their dreams. What will Kleinfeld's customers do when they meet? No. No. Really? Looks terrible. Next. I hate it. But, I love it! Well, it's my wedding, too! Reporter: Our groom is sitting next to another family waiting for their bride to model dresses. Is her fiance here? No, he is at work like he should be. He doesn't want to look at the wedding dresses? Reporter: Well, our groom is different. Honey? Reporter: And here comes his bride-to-be. This is definitely not it. Why don't you like it? I like the lace. You look frumpy. You look like you're out of the 1700s. This is the dress that I've always dreamed of. Well, I'm sorry, it's not going to cut it. Reporter: It's back to the dressing room for our bride. And for this woman, the beginning of an intervention. You understand why it is such a big deal? I do, but you are making yourself crazy. She couldn't even get the cake right the other day. Color. It has to be perfect, why can't it be perfect? Reporter: She's hoping this next dress will satisfy him. I hate it. I hate it. But it's a pnina tornai. I don't care what it is. I hate it! Reporter: He's clearly not easy to please. But she's one determined woman. What would you like? I don't know what I would like. But I will know it when I see it. Why don't you walk around and see what looks nice that's over here? Reporter: She even leaves her family to help him find something that will finally make him happy. You wanted something vintagey? No. I love that one. Babe, take that one off right now and try the other one. I trust this woman. Reporter: Maybe. Just maybe. He'll say "Yes" to this dress! This one is pretty. The dress is stunning. It's you. You're not stunning in it. Shh! This is the biggest decision of my life. And that is not stunning. Are you going to have children? That's the biggest decision. Your health that is the biggest decision. Her being happy is the biggest decision. That's the most important thing. Everything else is fluff. I'm promising you. Fantastic. John Quinones. Yes you are! And this is what would you do? No! Where is he? Where is Dan? The dress is gorgeous. You chose well! He's just an actor. Oh, thank god. Tell her she's beautiful. You're beautiful. Reporter: Groomzilla's back. And so is his relentless pursuit of perfection. Look at your arms. I know, I know I'm working on it. 15 pounds. Three spin classes a week and I think maybe you fit in that dress. Okay. Now, guess who walks into our scene? It's the woman who created this dress. What's his name? Dan. Nice to meet you, I'm pnina tornai. Pnina tornai. Her gowns are Kleinfeld's best sellers. Known for their sexy corsets and dramatic price tags. John, this is the designer of the dress. She doesn't know that we're here. Holy cow. The dress is beautiful. I don't think she can pull it off. This woman is amazing. She has a beautiful shape. For me, the designer of the dress, please, let me say my word. You absolutely do justice to my dress. We've been to amazing weddings and this has to blow everyone out of the water. She will blow everyone out of the water already the way she looks. Reporter: And she doesn't stop there. I'm happy I'm not marrying you, because I would die. Nobody sees it the way I see it. Reporter: Groomzilla stomps away. Come here, come here. Reporter: And our bride is surrounded with support. You're amazing. He just wants it to be perfect. But we're human beings, you cannot be perfect. Reporter: Turns out her high end designs come with down-to-earth advice. Hi there. I'm John Quinones. The husband to-be was an actor. Good 'cause I was about to kill him! What do you say to someone like that? Well I think for people of that kind, being very straightforward and telling them what they are, in their faces, I think can help them. Reporter: Thankfully, he's not really a monster. She kind of joked, and said, I'm glad I'm not marrying you. Yeah, and he's handsome. You know what it takes for me to say that? Reporter: Throughout the day our bride is comforted by kindred spirits. This whole experience for everyone is so extremely stressful. I never fight with my fiance and then we got engaged and now we're like fighting. And it just, it just happens. Reporter: This woman tells him to go home. Stay home and let her surprise you that day. Let her pick out the dress. Reporter: And some share their worries about the future. If he's like that now for a dress what is he going to be like in five years? I didn't want to tell her that she should break up with him, but she should, I wanted to say that. I can't believe you're serious about this. Reporter: But no one intervenes quite like these women. What's wrong with it? You have back fat and if you didn't have back fat maybe all these dresses would work. It's a waste of time. Reporter: He leaves his bride in tears. And this fellow bride-to-be doesn't let her spend one moment alone. You look beautiful. I know you love him but it's not right. Truthfully you look really beautiful. I just want him to be happy. Well, you should be happy! You shouldn't feel this way trying on wedding dresses! Her future mother-in-law goes one step further. You pick the dress that you want to wear and if he doesn't like it then don't friggin' marry him. Really. Reporter: Now, our groom returns. You are not a nice person. If you were my husband I would not be marrying you. You should like her even if she wears pajamas to her wedding. Reporter: Looks like groomzilla finally met his match. I feel like I am in a movie. Me too. You're not in a movie, but it's "What would you do?" The TV show. What was going through your mind? How we just wanted him to leave. And her never, ever, ever to marry him. I couldn't believe it and I'm sure things like this happen. Your advice to brides who are faced with this sort of thing? Say see you later. Reporter: And advice to groomzillas everywhere, don't let the monster in you stomp your way back to single. Coming up --
This transcript has been automatically generated and may not be 100% accurate.