Over the years, NCIS has given fans the occasional flashback episode, where "Gibbs" and "Ducky" venture back several decades on-screen.

To do so, Mark Harmon, 69, and David McCallum, 87, pass off their roles to younger stars. Fans love seeing Harmon's son, Sean, fill in as the young "Gibbs," but who is that playing the young "Ducky," seen again in the episode 400 special?

NCIS episode 400: Young "Ducky" actor Adam Campbell

While "Gibbs" stays in the family with Sean Harmon, young "Ducky" actor Adam Campbell is not actually related to the legendary Mr. McCallum. But in total, Campbell has played young "Donald 'Ducky' Mallard" in four episodes—one in 2014, 2015, 2016, and now again in 2020.

Campbell was also joined in the second episode of season 18 by Sean Harmon, who was portraying young "Gibbs" for the seventh time on NCIS, but the first time in eight years. Here's what to know about Campbell, a British actor.

Adam Campbell: Movies and TV shows beyond NCIS

Campbell is a 40-year-old star from Bath, England. Here are five facts about him:

  • His best-known work includes Unbreakable Kimmy Schmidt and Great News
  • Campbell married Glee actress Jayma Mays in 2007
  • His first NCIS episode aired in season 12, when he was 34 years old
  • He was cast to voice Ringo Starr in a cancelled Beatles film
  • The actor will next appear in a 2021 TV series titled Piccolo
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NCIS actor Adam Campbell and wife Jayma Mays

NCIS won't air the follow-up to episode 400 until Tuesday, Dec. 8. It's thought episodes could come with occasional delays amid the pandemic and it's already known season 18 will be a few episodes short due to the late start.

NCIS and NCIS: L.A. Will Resume Production In September

Quiz

Which 'NCIS' character was NOT first introduced in 'JAG'?