Rich Cronin, lead singer for the musical group LFO, passed away this week after a long health battle. He was 36 years old.

Rich, who penned the trio’s breakout hit “Summer Girls,” was diagnosed with leukemia in 2005. Despite a number of setbacks—including chemotherapy, a stem cell transplant, a stroke and a return of the disease—Cronin was able to perform again with his former band members last summer.

“He was so happy,” Brad Fischetti told EW about Rich’s return to the stage. Although the group had hoped to hit the road again later this year, Cronin found himself back in the hospital.

“We really became soulmates,” Brad recalled about their last tour together. “Devin [Lima] and I both realized how much we loved him, despite the differences we had in the past. In New York City at the Highline Ballroom, he thanked the crowd at the end of the show. I’ll always have that voice in my mind, because it was such a sincere thank you. Really, that’s the memory that’s sticking out in my brain.”