Glen Campbell's final live performance is a testament to his enduring monumental talent, but it's also a stark reminder of the power Alzheimer's disease has to take away everything that a person holds dear.

Campbell revealed his Alzheimer's diagnosis to the public in 2011, and he set out on his Goodbye Tour as a way to say farewell to his fans before the disease robbed him of his ability to play and sing. He captured the tour in a film titled Glen Campbell: I'll Be Me, and the clip above shows the iconic entertainer in the very last live performance of his lifetime, performing "Gentle on My Mind" at Uptown Theatre in Napa, Calif., on Nov. 30, 2012.

Alzheimer's had really begun to take its toll on Campbell by the end of the tour, forcing him to repeatedly cancel and re-schedule dates. His struggle against his own mind is clearly evident in the clip as he stands at the mic, bantering with the audience as he struggles to recall the familiar opening lines to the song he turned into a career hit in 1967 and performed thousands of times over his career.

When Campbell finally does manage to find the words, his voice is still as strong as ever, but he fumbles through the lyrics, jumbling different verses together at random before breaking off into a guitar solo. There, too, he demonstrates remarkably sharp playing skills for a performer his age ... but then goes off the rails into a jumble of incorrect notes before recovering, only to stop playing altogether and comment on the quality of his guitar tone into the mic, complaining that that it has too much treble and is "way too thin."

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"That was a really difficult day," Campbell's wife Kim says in the clip. "It was difficult leading up to the show, it was really stressful and difficult. That night was really, really, really hard, and we just knew this was it. We were going home for the Christmas break, and that we were not gonna add more shows after that."

Campbell died on Tuesday (Aug. 8) at the age of 81 from Alzheimer's complications. He was living full-time in a Nashville care facility, and his daughter Ashley admitted that he had deteriorated to he point that he didn't even know that his final album, Adios, had been released in June.

"We don’t want to sugarcoat it," she told the Boot. "He has no idea that he has an album out. He had no idea when he won a Grammy."

Tributes have poured in from fellow musicians, including Keith Urban, who praised Campbell's musical influence on him, while Jake Owen turned to Facebook Live to perform a cover of "Wichita Lineman." John Mayer gave the crowd at his Nashville gig on Tuesday night a stellar cover of "Gentle on My Mind," calling it "my favorite song in the world."

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