It's fitting that for its 100th episode, "The Vampire Diaries" deals with the most human of conditions: aging.
The CW series returns from its winter break with a milestone episode, "Five Hundred Years of Solitude." "It's a big accomplishment that not many shows can say that they have reached," star Nina Dobrev (Elena/Katherine) told Yahoo TV and other media outlets on the Atlanta, Georgia set last fall.
Executive producers Julie Plec, Caroline Dries, and Kevin Williamson "did a really great job of making a great episode of television," Dobrev said, "and also catering to the fans and giving them what they would like to see and would make them happy — paying homage to many past episodes, experiences, characters."
Here are seven things to know about the game-changing 100th episode:
1. It's all about Katherine.
"Five Hundred Years of Solitude" focuses on Katherine, the once haughty vampire-turned-human who's been aging this season — a process that she hasn't handled well.
"She was — and is — a very vain, selfish person. So for her to get a gray hair, lose a tooth, get wrinkles, and start to age, it's terrifying," Dobrev noted.
"She's starting to realize she has no friends. She has no family. She has no loved ones. She has no one that really cares about her because she's never cared about anyone but herself."
2. Nobody's crying much about Katherine possibly dying.
Katherine's bad behavior has earned her quite a few enemies, and the other characters in the show relive some of the vamp's most notorious moments.
"Damon wants Katherine as dead as a doornail," Ian Somerhalder said. "I think she reminds him of everything awful he's ever done — she taught him how to kill, taught him how to enjoy it."
[Related: Know Your Steve McQueens!]
3. The past is present.
The episode also flashes back to 1490, the night when Elena gave birth to her daughter, Nadia, who was immediately taken from her. The flashbacks will provide new insight into perhaps the most heartless character in the series.
"It's a really great look at this character, because if you really look at it, she's the root that started this whole thing," noted Candice Accola (Caroline). "The only reason Stefan stopped in Mystic Falls was because he thought he saw Katherine. The only reason Damon returned to Mystic Falls was because he was looking for Katherine. The only reason Caroline is a vampire is because of Katherine. The only reason Damon and Stefan ever became vampires was because of Katherine, so she's kind of the root."
4. Look who's back!
All that walking down memory lane means the return of some familiar faces. Who may pop up? That's top secret for now, but let's just say we spied quite a few former cast members at the 100th episode party, including Matt Davis (Alaric), Sara Canning (Aunt Jenna), and Kayla Ewell (Vicki Donovan).
"As you know on 'The Vampire Diaries,' nobody's really dead," laughed Michael Trevino (Tyler).
5. Someone tries to save Katherine's life.
Clearly, it isn't Damon and probably not Elena. Rather, it's Nadia, her long-lost daughter.
"Nadia is fighting to take care of her and have her in her life, but Katherine keeps doing things to piss her off. She's just not good at thinking about other people," Dobrev said. "But you learn that she actually does want to have it, she does want to have that relationship. She just keeps screwing it up."
6. Damon and Elena are still broken up.
In December's winter finale, Damon broke up with Elena by saying he was bad for her. Well, he hasn't changed his mind. When she insists she's not perfect, either, he lashes out at her. "Stop defending me! I can't change who I am, but I refuse to change you," he yells in an extended preview.
While Caroline is gleeful that the two are over, it's actually Stefan who urges Elena to stick with it.
"You didn't give up on me, so don't give up on Damon," he tells her. Wow, these two have come a long way!
7. Prepare for tears and heartbreak.
Paul Wesley (Stefan) described the 100th episode as "very emotional." Meanwhile, Kat Graham (Bonnie) warned us that fans are "going to lose their minds."
"The fans are going to be in ecstasy when they watch it. I don't think I've ever used that word," she said.
"There are some things that happen in the 100th episode that are going to make a couple people stand on their couches and scream at their TV, 'Yes, yes, yes!'"
We can't wait for No. 100!
"The Vampire Diaries" airs Thursdays at 8 p.m. on The CW.