Eric Millegan T.J Thyne Bones FOX

TV Query: Who is Zack Addy on ‘Bones’?

Unless you’re a veteran fan from the early years, that mind-blowing “Bones” finale might have you asking, “Who in the world was that guy?”

The answer lies in the first few seasons of the show, when Brennan (Emily Deschanel) had an adoring assistant by the name of Zack Addy (Eric Millegan). He was an exceptionally brilliant student, whose stellar IQ allowed him to accumulate multiple degrees at a young age.

RELATED: TV Query: Is ‘Bones’ T.J. Thyne paralyzed in real life?

Millegan appeared as a series regular on the first three seasons of “Bones,” oftentimes paired in scenes and storylines with his BFF Hodgins (T.J Thyne) to help solve cases. He exited the series when Zack decided to use his brains and ingenuity for evil and teamed up with a serial killer, The Gormogon (Laurence Todd Rosenthal).

During a final confrontation with The Gormogon, Zack received third-degree burns to his hands while helping his sadistic new mentor steal a skeleton from the lab. After his injury, Zack realized how deeply he’d been manipulated and pleaded insanity to his murder charges, which is how he ended up in a mental institution rather than jail.

Now, Zack’s long-time crush on Dr. Brennan seems to have come back to bite them all, as he’s been revealed as the genius marionette killer the team has been hunting in Season 11.

RELATED: TV Query: How many speedsters are on ‘The Flash’?

We’re actually ashamed that we didn’t put the pieces together sooner! Hodgins (T.J. Thyne) has commented multiple times that this killer must have an IQ off the charts, and his trick with the muddy boots proved that he had knowledge of investigation protocol and how the team works.

Plus, Zack’s earlier crimes prove that he’s unstable and perfectly capable of murder. We’ll have to wait and see if “Bones” throws us all for a loop and proves him innocent next season, but right now the evidence is definitely piling up.

“Bones” is set to return in 2017.