Phil Everly - who with his brother, Don, made up the revered US rock and country duo - has died aged 74.
He passed away in the Los Angeles suburb of Burbank following complications from chronic obstructive pulmonary disease, his wife Patti told the LA Times.
She said the disease had been contracted through a lifetime of smoking and the family were "absolutely heartbroken".
The Everly Brothers, with their high, close-harmony singing, had 19 Top 40 hits during their heyday between 1957 and 1962.
Their songs include Bye Bye Love, All I Have To Do Is Dream, Cathy's Clown and Wake Up Little Susie.
They profoundly influenced 1960s-era groups and singer-songwriters ranging from Beatles John Lennon and Paul McCartney, who early in their careers called themselves the Foreverly Brothers, to Simon and Garfunkel, the Byrds, the Hollies and the Beach Boys.
"Perhaps even more powerfully than Elvis Presley, the Everly Brothers melded country with the emerging sound of Fifties rock & roll," Rolling Stone magazine said in placing the brothers at No.33 on its list of the 100 Greatest Artists.
Tributes have poured in for the youngest of the duo.
Rock and country singer-songwriter Charlie Daniels tweeted: "Rest in peace Phil Everly. You guys brought us a lot of pleasure back in the day."
Linda Ronstadt, who recorded one of the biggest hits of her career in 1975 with her interpretation of the Everlys' When Will I Be Loved, said: "They had that sibling sound. The information of your DNA is carried in your voice, and you can get a sound (with family) that you never get with someone who's not blood-related to you.
"And they were both such good singers -- they were one of the foundations, one of the cornerstones of the new rock 'n' roll sound."
Lyricist Sir Tim Rice posted on Twitter: "Death of the great Phil Everly one of the saddest musical exits of all time for me. He and Don more influential than even they knew."
Green Day's Billie Joe Armstrong wrote: "The Everly Brothers go way back far as I can remember hearing music. Those harmonies live on forever. We're gonna miss you Phil. Gratitude."
Singer Nancy Sinatra, daughter of Frank, tweeted: "Touring with Phil and Don was one of the thrills of my life. I love you Phillip - Godspeed."
Don was born in 1937 in Brownie, Kentucky, to Ike and Margaret Everly, who were folk and country music singers.
Phil was born to the couple on January 19, 1939, in Chicago where the Everlys moved to from Brownie when Ike grew tired of working in coal mines.
The brothers began singing country music in 1945 on their family's radio show in Shenandoah, Iowa.
Their career breakthrough came when they moved to Nashville in the mid-1950s and signed a recording contract with New York-based Cadence Records.
In all, their career spanned five decades, although they performed separately from 1973 to 1983 after a dramatic onstage break-up during a concert in California.
Phil threw his guitar down and walked off, prompting Don to tell the crowd: "The Everly Brothers died 10 years ago."
During their breakup, they pursued solo singing careers with little fanfare. Phil also appeared in the Clint Eastwood movie Every Which Way But Loose.
After their decade-long estrangement, the brothers reunited in 1983 - "sealing it with a hug," Phil said at the time.
They were inducted into the Rock 'n' Roll Hall of Fame in 1986, the same year they had a hit pop-country record, Born Yesterday.
Speaking in an interview in 1986, Don said the duo were successful because "we never followed trends".
He added: "We did what we liked and followed our instincts. Rock 'n' roll did survive, and we were right about that. Country did survive, and we were right about that. You can mix the two but people said we couldn't."
Phil is survived by Don, wife Patti, mother Margaret, sons Jason and Chris, and two granddaughters.
:: Watch Sky News live on television, on Sky channel 501, Virgin Media channel 602, Freeview channel 82 and Freesat channel 202.