Nicky Wonder, Brian Wilson’s longtime guitarist and one of the founding members of the power-pop band the Wondermints, has died, Rolling Stone reports. He was 59.

“Today is a sad sad day,” Wilson wrote in a statement. “It is with my deepest regret to tell you that our beloved Nicky Wonder passed away last night in his sleep. We are in a state of shock as you can imagine. But we are going to honor him with tonight’s show. Nicky was my favorite guitar player ever. I always loved the way he used his fingers. He was a real Rock and Roll guy and great singer too. He was a friendly and very nice person and he was really really funny. He had the best sense of humor. We are all crying today, he will be missed beyond words. Our hearts go out to his wife Susan and his entire family, friends and fans. We love you Nicky.”

Nick Walusko started the Wondermints in 1992 with Darian Sahanaja. Their debut self-titled album arrived in 1995, and their last album was 2002’s Mind If We Make Love to You. They famously contributed the theme song to Austin Powers.

In 1999, they became Wilson’s touring band and contributed to many of his albums. Most notably, Walusko and the Wondermints played on his 2004 album Smile—the long-awaited finished version of his iconic lost Beach Boys album.