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What Only Hardcore NCIS Fans Know About Abby's Family

If Abigail "Abby" Sciuto (Pauley Perrette) is one of your favorite characters on CBS's long-running investigative drama NCIS, you already know that she has a strong personality, she knows sign language, and she has a particular favorite caffeinated drink (it's the fictional Caf-Pow, by the way). 

As the dedicated forensic technician, Abby's brilliant, and she often provides crucial details about how to crack a case, but she also has a heart big enough for the entire NCIS team, as long as they don't do anything to get on her bad side. Even though Abby seems to be an open book — always rocking her signature style and speaking freely about her sometimes-far-fetched beliefs — fans still got to discover quite a few of her secrets while she was on the show from 2003-2018

However, there is still something that only hardcore NCIS fans know about Abby's family. Don't worry — we've got the scoop to fill you in.

Abby's family on NCIS isn't her biological family

As Screen Rant notes, Abby discovers in season 9 of NCIS that her family isn't her biological family — she's adopted!

In the season's fourth episode, entitled "Enemy on the Hill," Abby has some tests done to become an anonymous kidney donor for a stranger in need, when she gets some unexpected news about her own family. Abby is told that someone else has also been screened to become a donor, and that the person in question has 99.9% similar DNA to her own. This leads Abby to question her brother, Luca Sciuto (Cole Sand), about him becoming a donor, but when he says it wasn't him, it sends Abby on a mission to find out who submitted the matching DNA.

As she tells Dr. Donald "Ducky" Mallard (David McCallum), "We had to give a mitochondrial DNA sample. Ours was a dead on match, Ducky — more than 99.9%. I mean we have to be full-on brother and sister, right? I pressed the coordinator for details on the guy, like his name and address, but she clammed up."

Only hardcore NCIS fans know how Abby discovered she was adopted

Later in the episode, McGee (Sean Murray) finds out who the mystery donor is, and Gibbs relays the information to Abby. She decides to meet the man, Kyle (Daniel Louis Rivas), and she reflects that her own loving family would not have given a child up for adoption, and she decides to do something she hadn't ever considered. Abby compared her DNA to a hair sample of her mother's, which she had been carrying with her in a locket, and she makes the surprising discovery: They don't match. This leads Abby to the conclusion that she had actually been adopted by what she had always thought was her biological family.

Abby opens up to Leroy Jethro Gibbs (Mark Harmon) about what she discovered. She says, "This whole brother/sister thing, it didn't make any sense to me. I mean, Kyle and me, our DNA is a total match. So we have to have the same biological parents. So then I was like — what? Did they give him up for adoption. I can't imagine the wonderful loving parents that raised me and Luca ever giving up a child. But they would have adopted a child — and they did — me ... I'm adopted, Gibbs."