Transcript for John Green discusses his new book 'Turtles All The Way Down'
book called "Turtles all the way down" and already the number one best-seller on Amazon. We'll talk to him after a quick look at his blockbuster success. Good morning. Reporter: John green is the king of young adult novels. The first chapter of "Turtles all the way down." Reporter: Selling more than 50 million copies worldwide. His blockbusters include looking for Alaska, paper towns and the fault in our stars. He also stays connected to fans online with nearly 6 million Twitter followers and two wildly popular YouTube sites. I have obsessive compulsive disorder. Reporter: He personally reel veried his struggles. In his new book "Turtles all the way down" green tackles mental illness head on. And John green joins us right now. Thanks for coming in again today. You just had that confession. We just saw in your YouTube video but your main character in the book suffers from OCD. Ye, she has obsessive/compulsive disorder and feels like she has thoughts that she can't get rid of that kind of feel like they're coming from the outside of her and then she uses compulsive behavers to try to manage these thoughts that she can't stop having. So you get inside the mind and the heart of a 16-year-old girl. So important to so many young women who are struggling with anxiety. A lot have apgs sitety disorders and a lot live with obsessive thought problems. I'm one of them and one of the reasons I wanted to write the book is because you know I did feel very alone in that for a long time. I think that psychic pain can be tremendously isolating and that only compounds the hurt of it. That's got to be one of the most fulfilling things about your job helping people to feel less alone with their issues. Yeah, I mean I love writing books. I love making videos. I feel incredibly lucky to be able to do it. It does. I love being able to connect with people and help connect people to each other. What's the most important thing you hope people get out of this one. I hope people understand maybe, get a glimpse of what it's like to live with mental illness. This kind of mental illness and I also hope people who may be love someone who has a mental illness or, you know, we all know that experience of wanting to take pain away from our kids, those of us who have kids and writing about that was really important to me. When I was a younger writer I didn't care as much about parental characters as I do now that I'm a parent. So writing about the relationship between parents and children in this book was really important. Got a lot of fans. Your nerd fighters including Seamus. He's got a question. So, I had a question for you. How did your interactions with nerd fighters sort of shape your writing of the book? Well, I mean it shaped my writing of the book so much in so many ways. I mean, the great thing about my job I get to hear from teenagers and young people every single day and YouTube comments and that's really helpful but also I was writing for you guys when no one was reading it in these like coded blogs that only a few people could read and that was super helpful to me because I was able to write for a really small audience that was generous so thank you. You get to communicate in two different ways. You write alone all morning then go do the videos in the afternoon. Yeah, it's perfect for me because I get to spend a lot of time alone in my basement which is great. And then spend my afternoon connecting with people directly online. You're going to connect with millions with "Turtles all the way down." John green, thanks for coming in. Thank you. Everyone should know everyone here in the audience is going home with a copy.
This transcript has been automatically generated and may not be 100% accurate.