@panzade,
You caught in me in mid-edit. John ( real name Deutschendorf) Denver was linked to the group. Randy Sparks provided a fast-track to find suitable replacements to NCM largish stable of performers. In John's case, he went solo before he actually became part of that group. FWIW, John D's uncle Dave did become a more recent NCM member.
Yes, it is true that he was part of Chad Mitchell Trio.
After Chad left the CM Trio,
" ... Mitchell left the trio in 1965 to embark on a solo singing career. Another audition process replaced him with the young (and unknown) singer/songwriter John Denver. The group retained the well-known "Mitchell Trio" name, with Denver writing some of the group's songs."