Guitarist Brian “Head” Welch was at the prime of his career during the late ‘90s and early 2000s when Korn helped define a completely new genre of music known as nu-metal, becoming one of the most successful acts of its day.

But behind closed doors, the Grammy-winning rock star was losing himself to drugs and alcohol.

Welch walked away from Korn – and a $23 million dollar record deal – in 2005 after he found God. The bold move helped him become free of his addictions, but the single father still needed plenty of saving.

The now 48-year-old and his daughter, Jennea Welch, are the subjects of a new Showtime documentary titled “Loud Krazy Love,” a shocking tell-all about his complicated relationship with the now 20-year-old who was also privately battling her own demons. It features in-depth interviews with the pair, with Welch’s parents and also with his bandmates.

Welch told Fox News filming technically began in 2005, after MTV reached out about creating a spirituality show. But when the project fell through, Welch kept the footage until 2013 when the idea of a film exploring his life with Korn was presented to him. However, it was clear to Welch that the real story he was ready to share was the one that even his die-hard fans didn’t know about.

In the film, Welch revealed that despite having it all – fame, fortune and a child he adored – he was still suffering from unhappiness.

“I think the root was the self-hatred that was going on due to unresolved issues growing up,” Welch explained. “I didn’t have the best relationship with my dad. I was bullied in school, picked on. I remember the first time of just trying to connect with girls. It was just rejection after rejection. So I always felt ugly. … Every time I looked in the mirror, it was like, ‘You’re not good enough.’ ‘There’s always someone more popular.’ ‘There’s always someone more gifted in music.'

“… I feel like I was too sensitive to things. And they would get to me. And I would let them just tear me down. And no matter how successful I got later on, I just felt like, if people really got to know me, got close to me, they wouldn’t like me. That’s the lie I believed about myself. And so I would just mask it with drugs and alcohol for years and years… It wasn’t until I found my faith that I learned to love myself.”

The Hollywood Reporter revealed Welch’s addictions became so severe he would hide his crystal meth in vitamins, deodorant – whatever was handy – while touring with Korn. Welch also shared on Matt Weiss and Theo Von’s “Allegedly” podcast that he once sent 1/8 ounce of crystal meth via Fed Ex.

Jennea had an unconventional childhood, one that involved hitting the road as a toddler alongside her famous father on tour.

“When I think about being on the road, it’s a lot of bittersweet memories honestly,” Jennea told Fox News. “We had so much fun. I was able to do whatever I wanted, eat whatever I wanted and just hang out. … There were promiscuous girls, parties and stuff. And I knew that it was wrong. But honestly, it was just what it was.”

But Jennea also endured loss. In the documentary, she vividly described moments in her young life when Welch was absent as he traveled the country with Korn. Then her mother, also dealing with addiction, left the pair behind. Jennea admitted it wasn’t easy to relive those memories of being alone.

“It was difficult,” she explained. “I think there were some sad things that as a kid I didn’t quite get. Because he wasn’t there and my mom wasn’t there. And I guess when I became older, it affected me a lot.”

When Welch converted to Christianity, he was determined to always be by Jennea’s side — but his struggles were far from over. He was no longer packing arenas and his finances were rapidly dwindling. Bad business deals also taunted Welch. Still, his faith endured.

“I was forewarned, I should say,” said Welch. “You go through trials, sometimes heavy ones. Sometimes it looks like God’s abandoned you, but not for any reason. [It’s] to make your faith grow and to see that no matter what happens, you come out OK. … It’s all for your good. It’s all for love and it’s all for making you a strong person.

“So when I lost my house, when I lost financing, when I lost cars and people betrayed me, it was just like the spiritual working out. I kept working hard to try to get things back on track and to see that I’m not going to need the band. The money is not who takes care of me anymore. God provides for me. … I come from a background where if someone is rough and tough, you handle things physically. People betrayed me and you just want to choke them. But you choose forgiveness.”

During her teens, Jennea found herself drowning in depression and anxiety. She resorted to cutting herself in hopes of eliminating a pain that refused to vanish. Jennea even considered taking her life.

“When I was 14, I was really open about my depression, anxiety on [social media],” she explained. “I was really open because I didn’t know how to talk to other people about it in a healthy way… I guess what made me want to share all these things [in the documentary] was the fact that so many other kids struggle. I talk to girls every day who are 14, 15, who battle with those things and battle with family dynamics. I just feel for them, and I feel like because I’m doing so well and I have so many healthy coping skills now, it would also be selfish not to share how far I’ve come.”

With the help of Welch, Jennea received intensive counseling. The Phoenix New Times reported Welch enrolled Jennea at a Christian boarding school in Lafayette, Ind., called Awakening Youth Academy. She credited the new environment for giving her a sense of normalcy.

“Boarding school helped me so much because I got to live just a normal life with some girls, some of my best friends,” said Jennea. “When I was younger, obviously it was difficult because there some things I was missing out on. [But] all that stuff has been restored.”

Jennea added she has reconnected with her mother over the years.

“We talk every once in a while, like every few months,” said Jennea. “We’re not super close, but I love her. She’s amazing and she’s been through so much.”

After nearly a decade apart, Welch reunited with Korn in 2013. Rolling Stone previously reported Welch received Jennea’s blessing to rejoin the group and pursue his passion for music.

As for facing temptation with drugs and alcohol, Welch said it’s not an option.

“I am done,” he stressed.

As for drinking, Welch admitted in his 2016 book “With My Eyes Wide Open” that there was a time where he couldn’t resist the bottle.

“I shared that I did start trying to drink again,’” he said. “I was like, ‘I’m not an alcoholic. After 10 years, I can have a couple of glasses of wine.’ And then that turned into binge drinking for a month or so. So yeah, I tried it and I was like, ‘I can’t do this. But before I quit, I’m gonna drink a couple more weeks.’ So I did not drink again.”

These days, Welch is perfectly content being sober and bonding with Jennea.

“I just don’t like it,” said Welch about his past vices. “I’d get these horrible hangovers where I’d feel massive, massive depression. So that helps me not drink. It’s just not for me. … I’m still a very practicing spiritual man. And I’m a Christian in the fact that I have a personal relationship with Christ. But there’s a lot of Christians that don’t understand me… That’s not going to stop me though. To me, God is love and God loves everybody and takes you as you are.”

“Loud Krazy Love” premieres Friday, Dec. 14 at 10 p.m. on Showtime.