Alex O'Loughlin and executive producer, Peter Lenkov, revealed a few details about Season 4 of Hawaii Five-O, which premieres on Sept. 27, in an interview with TVGuide.com.

The duo spoke about Steve McGarrett (O'Loughlin) trying to find out about how Wo Fat (Kigh Diegh) and his mother are related, the evolution of McGarrett and Catherine's relationship, McGarrett's dynamic with the new character Captain Grover (Chi McBride), and Danny (Scott Caan) and Chin Ho (Daniel Dae Kim) character arcs.

One of the main cliffhangers from the season 3 finale was the mystery of the connection between McGarrett and Wo Fat. McGarrett visited Wo Fat in a maximum security prison and discovered that Wo Fat was planning on using him as a human shield against enemies within the prison, who were trying to break into his cell.

In a preview clip for Season 4, McGarrett talked to Wo Fat in another maximum security prison at joint base Pearl Harbor. Half of Wo Fat's face was obliterated by raw burn scars. McGarrett asked Wo Fat about why his mother came to see him in prison, to which Wo Fat revealed that she came to apologize for kliing his father. McGarrett is left flabbergasted by this revelation. He then accused Wo Fat of killing her husband (his father), and hunting her for twenty years.

"He wants answers about his mother. And as far as he's concerned his mother's been dead for 20 years. There's something going on with Wo Fat and Doris McGarrett (Christine Lahti) and he can't get to the bottom of it, and so he goes to see him and we know what happens," O'Loughlin told TVGuide.

He went on to suggest that McGarrett and Wo Fat might be half brothers:

"The great sort of quandary for him is that he can't get past why Doris would have let Wo Fat escape that night back in the third season, in the house. It's not beyond imagination that they could be half-brothers. That's kind of eating him up. He's obsessed."

Watch the preview:

Tags: Hawaii Five-O Season 4 CBS