The Secret Circle stars Britt Robertson as Cassie, a young woman who discovers that she is a witch.
Harold has joined the cast as Charles Meade, the father of Cassie's new friend Diana (Shelley Hennig).
However, Harold told The TV Addict that Charles will hide his darker side.
"The bad guy villain gets really boring very quickly, but if you're that bad while being perceived to be that good, everywhere you look there's a potential disaster," he said. "It's interesting because I have to maintain a certain persona in public and in society but that's not really what I want. It's a means to an end."
Harold continued: "There is a very serious power grab going on where my character is, at least in the beginning, trying to reignite something through our children that we tried to do ourselves that went horribly wrong."
Harold, who explained that he hasn't read the LJ Smith novels upon which the series is based, added that he is excited about where Charles will go in the future.
"What I'm looking forward to most is learning how far down he's going to go, how much trouble he's going to cause and how he's going to get himself out of it," he said. "I hope that he really gets under someone's boot so he has to fight himself out of that all the while trying to be a good father, handle some legal issues, and walk down the street smiling."
Chris Zylka recently signed up for a guest role in The Secret Circle, which will premiere on September 15 on The CW.
> Britt Robertson: 'Secret Circle role is challenging'
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