Jamiroquai singer Jay Kay has left an emotional Facebook tribute to the band's original keyboardist, Toby Smith, who died on Tuesday.
The acid-jazz frontman, who rose to international prominence with the 1996 breakthrough album Travelling Without Moving, said the band would not have existed without his friend's input and musical virtuosity.
The 46-year-old's cause of death has not been revealed, but Kay alluded to the musician's struggle against a "voracious illness", which Smith had shown signs of beating until a recent bout of ill health.
He said: "Yesterday, I found out the news I was hoping, and truly believed, would never happen, that my dear friend Toby, had passed away.
"My heart hangs so heavy with grief and pain, that I have found it difficult to write anything about this up to now.
"The recent success of the new album has paled into complete and utter insignificance to me on hearing this terrible news.
"Toby had fought this voracious illness with his own indefatigable and stubborn brand of spirit and courage for a very long time, and until fairly recently, had shown all the signs of beating it, only for it to take him away so cruelly from his wife, his children, his relations and his many friends."
Smith played with Jamiroquai for 10 years, between 1992 and 2002, and performed on some of the band's best-loved singles including 1994's The Return Of The Space Cowboy and 1996's Virtual Insanity, which brought the group widespread popularity in the US.
Kay, 47, said Smith's death had also taken him away from the "millions of people who have enjoyed his music", and reminisced about the musician's ability to make him "laugh and cry in equal measure", and the first moment he heard him play in a bedsit in 1992.
He continued: "He has been a huge part of my life.
"Without him, there would be no JAMIROQUAI, and as I write this, the moon is clear and bright in the sky, and I think of him how it should be, riding his mighty horse across it, leaving a trail of stars behind him.
"I will miss you so much Tobesman. I will always be so proud of you. Ride the wind buddy, nothing can stop you now."
The band's original bassist Stuart Zender, 43, also left a tribute to his former bandmate on Instagram, and said he was the "most talented" musician he had worked with.
He said: "I love you so much. My big brother Toby crossed over to the other side last night.
"All my fondest memories are of him and the band that we created. The most talented musician I have ever had the honour to make music with.
"There will never be another like you Toby. Your light will shine on eternally. Thank you for making mine and everyone's life so bright."
Jamiroquai released their eighth studio album, Automaton, in March, and will embark on an international tour in May.