One direction may just be the biggest boy band on the planet or perhaps ever. With a new album and new tour, they're steering a billion dollar business. But even as they conquer the four corners of... See More
One direction may just be the biggest boy band on the planet or perhaps ever. With a new album and new tour, they're steering a billion dollar business. But even as they conquer the four corners of the earth, the boys will be boys. Backstage, they're already to bare all. And "nightline" co-anchor cynthia McFadden is there. Reporter: The biggest boy band in the world got up very early this morning and rocked a frigid central park. ♪ ♪ Reporter: A mega gma concert. This is how you roll? This is how we roll? Not this early? Or this cold? Their new album, "midnight memories" the number one album in 97 countries around the world. One single which has 50 million youtube hits is a highly personal ballad. ♪ The story of my life ♪ Reporter: "Story of my life." In part the new album is a response to criticism that the band doesn't write their own material. When weep sat down with them for an exclusive last they promised that was about to change. One of the criticisms, you play guitar, most are not playing instruments and not writing much of your music. Not true. Not true. Our next album, we wrote, what? 10 songs. 10 songs. I don't know -- ten songs. There are 13, 14. We wrote the majority. Reporter: Lyrics and music? Lyrics and melody. Reporter: To those who say they're a creation of simon cowl's x factor. We talked to ty colmer. He did have a hand in putting them together, you can't manufacture the success one direction had. They're having success that you see once in a generation. Reporter: Itch they're worried about overexpos overexposure it doesn't show. Last weekend they took home two american music awards. This is fan voted. We love our fans. You are incredible. Reporter: Last saturday was 1-d-day, seven hours of live streaming. Today they announced their 2014 north american stadium tour. This will be the biggest tour ever. Reporter: How do they prevent overexposure to the point where they're going enough. I think overexposure is something they aren't worried about right now. They are only looking to saturate the market even more. All of this on the heels of their highly entertaining documentary, this is us. We were permitted unprecedented access. Allowed where millions of teenage girls would love to be in their dressing room. Going to take a shower. Going to wear some jeans. Yeah. And a shirt. Very see-through. Reporter: While harry goes to shower. Nile is dressed by the stylist. There is a sense this is a safe haven. A place they can reveal? The first time we got. All of us got, just crosses. And, screws that keepup together. Keep you grounded thing. My mom hates tattoos. What does it say? One of the word from one of our new songs. A line from the new song. Reporter: Hold it. An exclusive. A line in one of the songs. I figured it out. I take it to heart. Every tim I se. It gets scary when you have load of people screaming. Reporter: They're trying to break the boy band mold. No matching outfits. No dancing. And so far, it certainly is working. Some say they could be the first ever billion dollar boy band. Why is one direction so successful? I think they have the full package. You have five, very talented, very good looking young men. And I think that they had the initial appeal, but then they have come out with just a string of really catchy and irresistible songs. I feel like -- they, they are actually getting belttter with each record. The band insists the music matters most. But the heartthrob aspect of the band's appeal is lost on no one. Certainly not them. Reporter: Any one show me a tattoo we haven't seen before. What have we got? Ha-ha. I'm not going to stop you, harry. You are absolutely kidding, but it was exciting for a minute. Reporter: You can't blame a girl for asking. For "nightline," cynthia
This transcript has been automatically generated and may not be 100% accurate.