Thomas, a flautist and vocalist, died suddenly at home in Surrey, England, on Thursday, according to a statement released by Cherry Red Records and Esoteric Recordings.
“We are deeply shocked by his passing and will miss his warmth, humour and kindness,” the label said.
“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.”
Thomas revealed on his website in 2014 that he had been diagnosed with prostate cancer the previous year.
“My cancer was in-operable but I have a fantastic doctor who immediately started me on a new treatment that has had [a] 90 percent success rate,” he wrote.
“The cancer is being held in remission but I’ll be receiving this treatment for the rest of my life.”
Thomas rose to fame in the 1960s and 70s after founding The Moody Blues with bandmates Mike Pinder, Denny Laine, Graeme Edge and Clint Warwick.
The band — whose hits included Go Now, Nights In White Satin and Question — have been chosen to be inducted into the Rock and Roll Hall of Fame in 2018.
Thomas, who started out in blues and soul music groups, also enjoyed some solo success with the albums From Mighty Oaks and Hopes Wishes And Dreams.
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