As one of the co-writers of Avicii’s hit song, “Wake Me Up,” Incubus guitarist Mike Einziger knew the Swedish DJ (real name: Tim Bergling), who died Friday of undisclosed causes at just 28, very well. Einziger says there are several unreleased songs they wrote together “I am hoping someday people will get to hear because, to me, they are some of my favorite pieces that I’ve ever written.” Einziger — pictured left above in 2013 with Avicii and Chic cofounder Nile Rodgers — spoke with Variety over the weekend and emotionally recalled his friendship with Berglinger and their work together.

I met Tim in 2012. We had friends in common, specifically [Avicii’s A&R rep] Neil Jacobson, who was helping him decide on musicians for the album. I was aware of who Tim was but I wasn’t very familiar with his work; I knew “Levels” and I knew that he was this really young kid who produced this amazing song that was really pervasive in pop culture. I wasn’t looking to write EDM music or anything like that, but when I heard Tim wanted to meet up to talk about music I thought it’d be a great opportunity for me to widen what I was working on. I thought it would be interesting to see where his head was at.

When we got together for the very first time, we didn’t make any music, we just talked for a few hours. And it was really obvious we should write together. Tim was telling me he wanted to make music in a much more organic way and he really wanted to utilize live instrumentation, he wanted to use his folk influences as a point of reference. He listened to really good music.

We made a plan that he would come over to my house and we would just spend an evening writing, so he did — and that was when “Wake Me Up” happened. It only took a few hours. It was like this splash of magic that is pretty unbelievable now, especially looking back on it: The first time we ever sat down to write music together, “Wake Me Up” happened.

I remember Tim sent me a rough mix of the song at like three o’clock in the morning — he’d continued working and editing and making little changes — and I played the song loud in my house. It felt really special. From that point on it was a groundswell: I played guitar and helped him on a bunch of the other songs on that album, like “Hey, Brother” and “Addicted to You.” We got to know each other more through that process and then we wrote several other songs together during that time. I am hoping someday people will get to them because, to me, they are some of my favorite pieces that I’ve ever written.

As time went on more and more people started connecting with the song. It became this thing that not only connected with people around me, it connected with kids, grandparents, and their children. I can’t tell you how many people have told me that their children grew up listening to “Wake Me Up” — whole families. To me, that’s the most gratifying thing in the world, to bring joy in people’s houses like that. I never would have seen that if it weren’t for Tim and I feel really fortunate and lucky to have worked with him.

We spent a lot of time together writing music after that and I got to know him well personally in a very individual, private type of way. We shared a lot of intimate, deep conversations about things we’ve been through, challenges we’ve faced, and there are a lot of pressures that come along with the type of success he’s had. I wish he were still here.

The thing that I remember most about him is his childlike curiosity when it comes to music. That’s a thing that goes away when you get older, that’s the thing that is so hard to maintain in your life — not just with music, with anything — and he brought that childlike sense of wonder and curiosity out of me in the songwriting process. It was all new to him and it rubbed off on me, and I’m so thankful for that. It’s so easy to become jaded, and he was just wide open. There was an innocence about him, in that way, that is kind of put it difficult into words. He had no ego in any of the music we made; he just wanted the best music.

Tim’s sense of production was just so monstrous: He really knew how he wanted every tiny syllable to sound. His level of commitment, it didn’t matter how long it took, he would sit there and record a work so many times. I would be so tired — I would go home and he was still hung up on one syllable.

The last time I saw him [was two or three months ago]. Incubus just finished a tour in Asia and Australia and South Africa, and right before we left I was in the studio with Tim and the British singer, Emile Sande. He seemed happy and he was glad to be back in the studio. We were working on a couple of new songs. He just seemed like he was in a good place; he was excited about music.

I wish I could have been there to help him. He was such a sweet person and had such a long life ahead of him. Maybe I didn’t appreciate this as much as I should have when he was alive, but he really changed my life in a pretty profound way, as a collaborator, as a creative partner. Some of the work we did together is some of the music I’m most proud of in my whole life. We went through a creative period together that was really exciting and fun. When stuff like that happens it’s just like magic and really rare. To have shared that with him and just to see and be able to feel how vibrant he was as a human being and also as an artist, he had such a strong creative vision. He was so committed to every single piece he worked on. And it was really a privilege to be around that and share that with somebody so vibrant.

He was so sweet and such a visionary. I still can’t believe he’s gone — I’m still just trying to process it. It’s awful. He was such a sweet human being, genuine. He was so young. These are all cliches, but it’s just tragic. All I can do is shake my head.