David McCallum, the final surviving original cast member of NCIS, passed away at the age of 90. In his final scene on the show, he appeared via video link as his character, Dr. Donald "Ducky" Mallard, revealed a major plot point. Although it was believed to be his last appearance, McCallum never formally announced his departure from the series. Recently, NCIS bosses teased that he could potentially make a return. McCallum's character had transitioned from a regular role to sporadic cameos over the years.