Article continues below advertisementIs Mark Harmon Returning to 'NCIS'?Source: Sonja Flemming/CBSMark Harmon appeared on 'NCIS' for 18 seasons.Will NCIS fans see Special Agent Leroy Jethro Gibbs again?Four years after Mark Harmon left the hit series, CBS confirmed he will return during the first crossover event between NCIS and NCIS: Origins on November 11. The Veterans Day crossover will focus on Austin Stowell's younger Gibbs and his team as they investigate a naval officer's death in the 1990s, according to Deadline."I'm very proud of the storytelling that David [J.