Acclaimed jazz bandleader Ken Peplowski has died … and his sudden passing occurred right before he was to play on a cruise already at sea, TMZ has learned.

A passenger on The Jazz Cruise tells TMZ … the renowned clarinetist and saxophonist died yesterday. Ken was supposed to play on the cruise in the late afternoon with a quartet … and was a no-show. A search ensued and he was found dead inside his cabin. His death was announced prior to the big band main feature concert later that night. The ballroom was shocked … with a lot of gasps and then silence.

A statement from the niche cruise’s executive director, Michael Lazaroff, reads in part … “He was a great musician, but he was also one of the very best entertainers ever. I do not know any musician who respected the bandstand more than Ken. He was always prepared, love performing with his fellow musicians, and, man, could he play!”

A friend and radio station WBGO‘s former director of editorial content wrote … Ken had been “suffering from multiple myeloma” and the jazz icon “battled the often fatal disease with a unique combination of courage, fortitude and humor.”

The Jazz Cruise is planning a more extensive remembrance, per Lazaroff.

Ken was 66.