Ray Thomas has died aged 76.
The Moody Blues star's record label Cherry Red Records and Esoteric Recordings confirmed he passed away "suddenly" on Thursday (04.01.18) at his home in Surrey, south east England.
They said in a statement: "It is with profound sorrow and sadness that Cherry Red Records and Esoteric Recordings regret to announce that Ray Thomas, founder member, flautist and vocalist of the Moody Blues, passed away suddenly at his home in Surrey on Thursday 4th January 2018.
"We are deeply shocked by his passing and will miss his warmth, humour and kindness.
"It was a privilege to have known and worked with him and our thoughts are with his family and his wife, Lee, at this sad time."
Ray revealed in 2014 he had been diagnosed with prostate cancer but was in remission, and urged others to be tested for the disease.
He said: "My cancer was in-operable but I have a fantastic doctor who immediately started me on a new treatment that has had 90 per cent success rate.
"The cancer is being held in remission but I'll be receiving this treatment for the rest of my life. I have four close friends who have all endured some kind of surgery or treatment for this cancer and all are doing well.
"While I don't like to talk publicly about my health problems, after Alvin [Stardust]'s death, I decided it was time I spoke out.
"A cancer diagnosis can shake your world and your family's but if caught in time it can be cured or held in remission. I urge all males to get tested NOW. Don't put it off by thinking it won't happen to me. It needs to be caught early. It's only a blood test - a few minutes out your day to save yourself from this disease. Love and God Bless, Ray."
Ray recorded seven albums with The Moody Blues and famously played the flute solo on 1967 hit single 'Nights in White Satin'.
He also penned a number of their tracks including 'Veteran Cosmic Rocker', and dropped solo albums 'From Mighty Oaks' and 'Hopes Wishes and Dreams' when the band temporarily split in 1974.
His passing comes just months ahead of the group's induction into the Rock and Roll Hall of Fame later this year.