Country singer Glen Campbell is giving ABC News his first TV interview since being diagnosed with Alzheimer’s disease.The chat with “Nightline” anchor Terry Moran will air Tuesday on “ABC World News With Diane Sawyer,” ”Good Morning America” and “Nightline.”ABC News offered this preview: “They discuss Campbell’s illustrious career and how the star is dealing with the realities of the degenerative disease while preparing to embark on a final tour to say thank you to his fans.”“Ghost on the Canvas,” Campbell’s final studio album, will be out Aug. 30. And Campbell, who is in the early stages of Alzheimer’s, will use “The Glen Campbell Goodbye Tour” to promote the album.Campbell’s five-decade career includes such classic songs as “By the Time I Get to Phoenix,” “Gentle on My Mind,” “Galveston,” “Wichita Lineman” and “Rhinestone Cowboy.”The interview has personal importance to Moran, who lost his mother and grandmother to Alzheimer’s.