Complex sentence: The series was also the only time host Bill Cullen emceed a talk show format on a regular basis; prior to this, his only talk-show experience was as a guest-host for Johnny Carson on "The Tonight Show".
Split into simpler sentences: The series was also the only time host Bill Cullen introduced a talk show format on a regular basis. Before this, his only talk-show experience was as a guest-host for Johnny Carson on "The Tonight Show".