Why do Sage and Rebekah have a tense history?

When The Vampire Diaries returns on tonight, the show's newest character, Sage, won't just reunite with old friend Damon, but with past adversary Rebekah as well.   

"They have a tension and a history there," Claire Holt (Rebekah) told TVGuide.com from the show's Atlanta set. "You find out Sage is looking for Finn, Rebekah's brother, so there's definitely a bit of a hate vibe going on."