Transcript for 'Friday' singer Rebecca Black on lessons learned 9 years after song went viral
You know, I had this insane thing happen to me when I was 13. But now I have a story to share. Reporter: The song "Friday", took America by storm nine years ago. Lookin' forward to the weekend Reporter: At the center of it all, Rebecca black, just 13 years old, becoming an overnight celebrity, but also facing a terrible backlash. I became unbelievably depressed. And trapped in this body of what I thought the world would see me as forever. When I hadn't even finished growing. Reporter: Just this week, Rebecca's social media posts about that tumultuous time going viral. The 22-year-old writing this letter to her younger self on Instagram and Twitter in the hopes of helping others. I'm trying to remind myself more and more that every day is an opportunity to shift your reality and lift spirit. You are not defined by any one choice. Reporter: How did you get to this place of honesty with yourself? In order for me to have any sort of successful life, whatever you want to call that, there was a lot of emotional things that needed to be addressed. Reporter: She says she grappled with low self-esteem and pressure as a teenager. When did depression become a real thing in your sniend. I don't know if there was a specific moment. I just kind of found myself Reporter: Rebecca's upbeat song about the end of the week was recorded for fun. "Friday" was a flash in the pan for me. Christmas break, I'll have all my friends there and maybe my grandmother will see it. Reporter: Her mother paid music producers $4,000 to write this video. Over 100 million people watched it on YouTube. It became a cultural moment, inspiring spoofs. And providing fodder for late-night comedians. It's the day before Friday, the day after Wednesday, two days after Tuesday. Reporter: Katy Perry even asked her to be in the video for her song "Last Friday night." I got to work with Katy Perry and be on set of like a lady gaga music video. There were crazy things that made it feel positive. Reporter: But Rebecca says she was also bullied at school and online. Having people tell you that you don't belong where you want to be, that you should kill yourself. Having to then reflect on all of that as a teenager is an unbelievable experience. Friday, Friday Reporter: Back in 2011, ABC cameras were with Rebecca at her home at the height of her fame. At the weekend Reporter: She addressed her critices. Some had called it the worst song ever recorded. I don't think I'm the worst singer, but I don't think I'm the best singer. Reporter: Lady gaga famously came to her defense. I think Rebecca black is a genius, and anyone telling Hershey's cheesy is full of . Reporter: But she still faced an onslaught of cruelty online. You're so fat. And you'll never be pretty. You suck at singing. Reporter: And in person. When I walk by, they'll start singing "Friday" in a really nasally voice or they'll be like hey, Rebecca, guess what day it is! Reporter: The teasing became so intense, Rebecca opted to be home schooled. Her mother taking over as her It's hard to go to school when you are so famous, and to have kids constantly making fun of what's going on. Reporter: She got death threats. Reporter: At the time, the teenager seemed to be taking it all in stride. I've had a lot of experience with not being liked. I think if I hadn't had to deal with that in the past I totally would have handled this differently and I would have gone down in burning flames. But I, I've learned that you just can't let it get to you. When I first saw all these nasty comments -- Reporter: But it turns out all the bullying was getting to her. We played her that interview from 2011. I did cry. I felt like this was my fault. Um, it's hard to watch. Because I was just trying to be the hundreds of different types of people I thought everybody wanted me to be, all at the same time. I was just trying to survive. Poor thing. So many times I wish I could go back in time as the person I am now so I could tell her, like, you're going to be okay. Don't call me your sweetheart Reporter: Despite the vicious attacks, Rebecca has never given up on her career. She's now back in the studio working on her music. Don't call me a sweetheart actually Reporter: She gave "Nightline" this preview of the upcoming remix of "Sweetheart." R goals now. I'm going to keep writing music. I've never stopped. And it's been the one thing that has never let me down. I've shown myself time and time again that I have resilience, and I have strength, and it's possible to grow and change and learn and how cool is that? Reporter: For "Nightline," I'm Kaylee Hartung in los Angeles.
This transcript has been automatically generated and may not be 100% accurate.