The musician, who was one of the founding members of UK band The Moody Blues, died on Thursday after a long battle with prostate cancer.
His record label confirmed the star's passing with a statement.
This read: "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."
Thomas took a back seat on the band in 1999 due to ill health.
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Stars we've lost in 2017
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“It is with profound sorrow and sadness that Cherry Red Records and Esoteric Recordings regret to announce that Ray Thomas has passed away suddenly”
Cherry Red Records and Esoteric Recordings
It was confirmed in 2014 that he had been diagnosed with prostate cancer.
In a statement at the time, 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% success rate.
"The cancer is being held in remission but I'll be receiving this treatment for the rest of my life.
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"I have four close friends who have all endured some kind of surgery or treatment for this cancer and all are doing well."
He continued: "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.
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"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."
The star concluded: "It's only a blood test - a few minutes out your day to save yourself from this disease. Love and God Bless, Ray."
The Moody Blues were known for hits including Tuesday Afternoon and Your Wildest Dreams.