Glen Campbell will release his final project, Adios, on June 9, featuring the biographical song "Arkansas Farmboy" about his upbringing. Written by longtime collaborator Carl Jackson, the song was inspired by a story that Campbell once told his friend about his grandfather.

"Arkansas Farmboy" tells the tale of how Campbell's grandfather gave him a $5 guitar as a young boy, and Campbell learned to play "In the Pines" on it. The song was written while Jackson was on an overseas flight.

“He had told me a story about his granddaddy teaching him to play 'In the Pines' on a five-dollar guitar," Jackson tells Billboard. "That stuck out to me. I remember we were on a flight overseas, I think going to Australia, and it started popping in my mind, so I wrote it and played it for Glen. He always loved the song, which I was proud of, because it was about him. It means the world for me to hear him sing these lyrics."

Glen Campbell's Career in Pictures

Jackson says that the song describes Campbell well, and notes that the singer was comfortable in being just that — an Arkansas farmboy.

"He was comfortable in being that, but also meeting kings, queens, and presidents. Wherever he was, he was just Glen Campbell. He stayed the wonderful man he always was, and the best singer in the world," Jackson adds. "Doing this record means the world with me. To be able to work with him, and to do something for him that he couldn’t do on his own right now means a lot.”

Adios is Campbell's final album because he is in the late stages of Alzheimer's. He is 81.