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Jethro Gibbs's father Jackson Gibbs (played by Ralph Waite ) was a World War II US Army Air Force fighter pilot, as was Mark Harmon's real life father Tom Harmon.

In addition to Troian Bellisario, one of Donald P. Bellisario's children, who plays as McGee's sister, there is also one of his sons, Michael Bellisario, who played Charles (Chip) Sterling on the show.

Whenever we see flashbacks featuring young Gibbs, the younger version is played by Mark Harmon's son, Sean.