Jimmy Webb, the Bayville singer-songwriter who penned many of Glen Campbell’s biggest hits, including “By the Time I Get to Phoenix” and “Galveston,” promised in an open letter to friends and family that the late singer will be remembered for generations to come.

“This I can promise: While I can play a piano he will never be forgotten,” Webb wrote in a Facebook post. “And after that someone else will revel in his vast library of recordings and pass them on to how many future generations? Possibly to all of them.”

Campbell died Tuesday near Nashville after a long, public battle with Alzheimer’s disease. He was 81.

Webb wrote Tuesday night that even though his friend’s death had been expected since being diagnosed with the disease in 2011, it still “stings like a sudden catastrophe.”

“Let the world note that a great American influence on pop music, the American Beatle, the secret link between so many artists and records that we can only marvel, has passed and cannot be replaced — my friend and brother in music, Glen Campbell,” Webb wrote. “He gave me a great wide lens through which to look at music. I watched him in awe executing his flawless rendition of ‘The William Tell Overture’ on his classical guitar in his Vegas show . . . This was the one great lesson that I learned from him as a kid: Musically speaking nothing is out of bounds.”

Webb wrote that Campbell “lavished affection and gifts” on friends and family, but that his greatest gift was his music. “One of his favorite songs was ‘Try A Little Kindness’ in which he sings ‘shine your light on everyone you see,’ ” he wrote. “My God. Did he do that or what? Just thinking back I believe suddenly that the raison d’être for every Glen Campbell show was to bring every suffering soul within the sound of his voice up a peg or two. Leave ’em laughin.’ Leave them feeling just a little tad better about themselves; even though he might have to make them cry a couple of times to get ’em there. What a majestically graceful and kind, top rate performer was Glen on his worst night!”

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Webb said Campbell was also generous with credit for his music.

“When it came to friendship Glen was the real deal,” he wrote. “He spoke my name from ten thousand stages. He was my big brother, my protector, my co-culprit, my John crying in the wilderness. Nobody liked a Jimmy Webb song as much as Glen!”

Webb wrote that Campbell’s death has left him “full of grief.”

“I am writing because I think you deserve some sort of message from me but I am too upset to write very well or at any great length,” wrote Webb, who published his memoir, “The Cake and The Rain” in April. “It’s like waking up in the morning in some Kafkaesque novella and finding that half of you is missing. {My wife,] Laura and I would call upon you to rest your sympathy with Kim Campbell and her children Cal, Shannon and Ashley; his older children, Debby, Kelli, Travis, Kane, and Dillon; grandchildren, great- and great-great-grandchildren. Perhaps you could throw in a prayer for the Webb kids, Chris, Justin, Jamie, Corey, Charles and Camila who looked upon him as a kind of wondrous uncle who was a celebrated star and funnier than old dad.”