Klaus (Joseph Morgan) laid his family to rest but Stefan (Paul Wesley) stole their coffins in the show's last episode.
Plec has now revealed that the Originals - including Klaus's sister Rebekah (Claire Holt) and brothers Kol (Nathaniel Buzolic) and Finn (Caspar Zafer) - could be revived and cause problems for Klaus.
"At least one of those daggered Originals is coming out of those coffins," she hinted. "That will happen sooner or later."
Plec added: "Klaus, who has been very much in control of everything for quite a long time, suddenly now has multiple siblings to deal with."
Plec also revealed that Klaus will be getting a love interest, saying: "What he does in pursuit of that someone will be an interesting and enjoyable part of the next chapter.
"[It's] an opportunity to see a side of Klaus that we haven't gotten to see yet, which is him being attracted to somebody else... It's going to be lots of fun."
Morgan has previously joked that there are no romantic feelings between Klaus and Stefan on the show.
The Vampire Diaries returns with a new episode tonight at 8/7c on The CW.
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