Alice Cooper has issued an emotional farewell to his late collaborator Dick Wagner, calling him "irreplaceable." Wagner, who co-wrote 'Welcome to My Nightmare' with Cooper and played guitar on 1972's 'School's Out,' died today (July 30) at 71 from respiratory failure.

"Even though we know it's inevitable, we never expect to suddenly lose close friends and collaborators," Cooper said via Billboard. "Dick Wagner and I shared as many laughs as we did hit records. He was one of a kind. He is irreplaceable. His brand of playing and writing is not seen anymore, and there are very few people that I enjoyed working with as much as I enjoyed working with Dick Wagner. A lot of my radio success in my solo career had to do with my relationship with Dick Wagner. Not just on stage, but in the studio and writing. Some of my biggest singles were ballads what I wrote with Dick Wagner. Most of 'Welcome to My Nightmare' was written with Dick. There was just a magic in the way we wrote together. He was always able to find exactly the right chord to match perfectly with what I was doing. I think that we always think our friends will be around as long as we are, so to hear of Dick's passing comes as a sudden shock and an enormous loss for me, Rock N Roll and to his family."

Wagner struggled with his health for years, having suffered a massive heart attack in 2007, and then lapsing into a weeks-long coma. His latest setback followed heart surgery, which led to a lung infection earlier this month. He died while in intensive care at a Phoenix hospital.

Wagner also co-wrote Cooper's 'Only Women Bleed' and 'I Never Cry,' among others, while performing on albums like 'Goes to Hell,' 'Hey Stoopid' and 2011's 'Welcome 2 My Nightmare,' which included a final collaboration called 'Something to Remember Me By.'