Peter Tork, a member of The Monkees, has died aged 77, according to his official Facebook page.
The American musician had been diagnosed with a rare form of tongue cancer in 2009.
A post on his Facebook page said: "It is with beyond heavy and broken hearts that we share the devastating news that our friend, mentor, teacher, and amazing soul, Peter Tork, has passed from this world."
Tork was one of the founding members of 1960s pop band The Monkees, famed for hit songs such as Daydream Believer and I'm A Believer.
Tributes from the world of music began pouring in following his death.
Fellow Monkees star Micky Dolenz said: "There are no words right now...heart broken over the loss of my Monkee brother, Peter Tork."
— Micky Dolenz (@TheMickyDolenz1) February 21, 2019
The Beach Boys frontman Brian Wilson wrote on Twitter: "I'm sad to hear about Peter Tork passing. I thought The Monkees were great and Peter will be missed. Love & mercy to Peter's family, friends and fans."
Blur guitarist Graham Coxon hailed Tork as his "favourite Monkee", while American songwriter Diane Warren tweeted: "Thank U for giving me your love beads (it was the 60s!) when I was a little girl."
Oh no RIP Peter Tork. Thank U for giving me your love beads (it was the 60s!) when I was a little girl.
— Diane Warren (@Diane_Warren) February 21, 2019
American singer Carole King added: "R.I.P. Peter Tork."
The Monkees were a made-for-TV group who formed in Los Angeles and starred in their own self-titled series from 1966 to 1968.
Tork played bass guitar and keyboards and sang vocals in the band alongside Dolenz, Michael Nesmith and the late English singer Davy Jones.
Following The Monkees, Tork worked in collaboration with several musicians including George Harrison, for whom he played banjo.
There followed an unsuccessful period with band Release, and a spell in prison for drugs possession.
He later took part in reunion tours with The Monkees.
On Tork's Facebook page, a statement thanked fans for their "love, dedication and support of our 'boss'."
"Please know that Peter was extremely appreciative of you, his Torkees, and one of his deepest joys was to be out in front of you, playing his music, and seeing you enjoy what he had to share," it added.