What happened to David McCallum from NCIS?

NCIS returns for Season 21 but without former star David McCallum. He played Chief Medical Examiner Donald "Ducky" Mallard.

Related Keywords

Hollywood ,California ,United States ,Jimmy Palmer Brian Dietzen ,Brian Dietzen ,Illya Kuryakin ,Nancy Sinatra ,David Mccallum ,Byron Purvis Admedia , ,David Mccallum From ,Chief Medical Examiner Donald ,Jimmy Palmer ,New Orleans ,Great Escape ,