Legendary singer, songwriter, and guitarist David Crosby, who helped define the rock sound of the 1960s and '70s, died Wednesday night at the age of 81. The rock icon is a founding member of both The Byrds and Crosby, Stills & Nash.

A source close to Crosby confirmed his death to Rolling Stone. However, the source did not disclose any cause of death. The musician reportedly died after a battle with a "long illness."

His death shocked many fans as he was very active on social media the day before he died. According to Variety, in one of his final tweets, the musician joked about heaven, saying, "I heard the place is overrated... cloudy."

David Crosby's Iconic Career in Music That Lasted Decades

David Crosby was a founding member of the Byrds. While a guitarist for the band, he also contributed harmony vocals to some of their most iconic songs like "Eight Miles High," "So You Want to Be a Rock 'n' Roll Star," and "Turn! Turn! Turn!"

However, Crosby soon found himself having personality conflicts with the band's frontman, Roger McGuinn, which made him leave the band. He then formed another iconic group, Crosby, Stills & Nash, with Stephen Stills of Buffalo Springfield and Graham Nash of the Hollies.

The trio became a quartet in 1969 when Neil Young joined. The band was instrumental in the rise of folk rock, country rock, and the emergent "California sound" in the mid-70s. The hit songs of Crosby, Stills, Nash & Young band's "Almost Cut My Hair," "Long Time Gone," and "Déjà Vu" were written by Crosby.

Crosby had previously butted heads with other members of the band, even calling out Young, saying he was "the most self-centered, self-obsessed, selfish person I know." Young eventually left the band.

Crosby, Stills & Nash disbanded for good in 2016. David Crosby was inducted into the Rock and Roll Hall of Fame in 1991 with the Byrds and in 1997 with Crosby, Stills & Nash.

Former Crosby, Stills & Nash Bandmate, Wife, Remember Late David Crosby

David Crosby's widow, Jan Dance, also announced her husband's death in a statement published by Variety. His family said that at the time of his death, he was "lovingly surrounded by his wife and soulmate Jan and son Django."

Dance noted that "his humanity and kind soul will continue to guide and inspire us," adding that Crosby's "legacy will continue to live on through his legendary music."

"Peace, love, and harmony to all who knew David and those he touched," Dance concluded. According to The Guardian, his friend and former bandmate Graham Nash also offered a tribute on social media, writing that he felt "profound sadness" when he heard the news of Crosby's passing.

"I know people tend to focus on how volatile our relationship has been at times, but what has always mattered to David and me more than anything was the pure joy of the music we created together," he noted.

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Written by: Rick Martin

WATCH: Crosby, Stills & Nash Perform "Teach Your Children" - From Letterman