The actress, who says the cast knows little more than the audience about writers' plans, says she was as surprised as anyone the key plotline involving a "sun and moon curse" turned out to be a ruse for character Klaus, who is scheming to become a vampire/werewolf hybrid.
"Trust me, when I read that script and looked at those pages and saw that everything that they've all been doing for the last two seasons really has been all made up and a big joke; broke my heart," she said.
Dobrev thinks it was a clever move to make Klaus appear more diabolical.
"It makes Klaus that much smarter and that much more clever and ahead of the game," she said. "It's like a puppet show and he's orchestrating the whole thing."
The actress also reveals that the cast has come up with their own, unofficial name for the hybrid: a "wampire."
Dobrev co-stars with Ian Somerhalder and Paul Wesley, who play vampire brothers obsessed with her two characters on the show: the sweet human Elena and the evil vampire ancestor Katherine.
Because Elena and Katherine are both identified as doppelgangers, Dobrev says "it's assumed" she will eventually have to take on another role as their original. She acknowledges, however, that she has "no idea" if that will happen.
"I didn't even know that I'd be playing Katherine when I signed on the project," she said. "It just popped up in the script one day and now there's mumbling about this third character because of the whole doppelganger thing."