The actress, who joined the show as Rebekah this season, told TV Line that the family will be explored when the show flashes back to the Viking era.
The scenes are expected to feature Rebekah and her brother Klaus (Joseph Morgan) as well as Elijah (Daniel Gillies), who was stabbed with the Original-slaying dagger last season.
The flashbacks will also introduce guest star Alice Evans, who is joining the show as the Originals' matriarch.
"There's going to be a lot revealed about the Original family and where we came from," Holt teased. "You get to see how [Rebekah] interacts with her family and what it was like back then."
Holt explained that fans will learn why Rebekah and Klaus "became so close and why they are so loyal to each other" and teased that more about vampire killer Mikael (Sebastian Roché) will be revealed.
"You'll learn that there's a very good reason why they're afraid of him," she hinted. "It has a lot to do with their history and why they are the way they are... He's definitely a threat to them."
The Vampire Diaries airs on Thursdays at 8/7c on The CW in the US and on Tuesdays at 9pm on ITV2 in the UK.