A disoriented Glen Campbell struggled through a show, barely recognizing his own songs.

The review in the Indianapolis Star said it all: "Glen Campbell Gives Mystifyingly Bad Show."

But we now know what was really going on. The country music legend has Alzheimer's disease.

75-year-old Campbell and his wife, Kim are going public in the new issue of People magazine, on stands Friday.

"He's planning to go on tour later this year and his wife said that she didn't want people seeing him on stage thinking maybe he was drunk, or questioning why he forgot the lyrics to his songs," said People magazine Sr. Writer Joey Bartolomeo.

At the show in Indianapolis three weeks ago, Campbell used teleprompters so he could read his lyrics, but he still mangled the songs he's been performing for decades. One fan said, it was the "most heartbreaking performance I've ever seen."

Campbell now tells People magazine, "I still love performing for my fans. I'd like to thank them for sticking with me through thick and thin."