Huge Lost spoiler (or crazy theory?) about the Smoke Monster

Fifteen-year-old actor Kenton Duty—who played the mysterious blond island kid on ABC's Lost—confirms what we all suspected: He was the young Jacob, and he's got a theory about the Smoke Monster. (Possible spoilers ahead!)

Considering he has actually watched the show since the pilot, his theory comes from a unique vantage point.

"Jacob felt such a betrayal when he found his brother with the bloody dagger that had just gone through this mom," Duty said in an exclusive interview. "That's the only mother he's even known. That's why he ended up basically killing him. ... I personally think the Smoke Monster is just, in reality, his soul taken out of his hollow body."

The young actor sees last week's origin episode, "Across the Sea," as pivotal to the story the Lost writers are trying to tell. The episode explored the first 43 years of Jacob and his twin brother, the Man in Black, and gave us insight into why these characters are at odds with each other, he said.

"I think it shows the beginning of why everything transpired on this island," he said. "The sides of the good and the sides of evil. This season you've seen people split off to their own separate groups, [deciding what sides they're] actually going to choose."

While Duty can't (or won't) tell us any details about what's to come during the two final episodes (and three and a half hours)—beginning tonight at 9 p.m. ET/PT and concluding Sunday—before Lost ends forever, he did confirm that he appears in tonight's episode, "What They Died For." "That's going to be another fun, juicy episode for the audience," he promised.

Duty said working on Lost was "extremely memorable," but it wasn't always easy, especially in the beginning, when he was known only as "teenage boy."

"The biggest challenge from the beginning was not knowing who I was," said Duty, who didn't know he was playing a young Jacob until he read the script for last week's episode. "So I just had to take the current script that I was given and I had to interpret it in my own way. That was like the really cool part, because the writers are brilliant in that way, because they knew where they were going to take me. But no one on the show, not like Terry O'Quinn or Nestor Carbonell or Josh Holloway, ... no one knew who I would be," he said.

Once he learned he'd be playing the mysterious Jacob, a character who has been driving much of the action on the show in one way or another since the series began, other challenges presented themselves. Suddenly his role had to mesh with the adult Jacob, who is played by Mark Pellegrino (Supernatural).

"I had a lot of fun working with Mark, 'cause we would go and eat lunch together, and we'd talk about what we thought this certain part was about, and we'd exchange ideas on how to do a certain part and that helped a lot," said Duty. "I wanted to make it a seamless transition from younger to older, so I just watched how he did it, and that helped me figure how I needed to be younger Jacob."

Duty (The Jay Leno Show, Cold Case) also got to work with his good friend of three and a half years, Ryan Bradford, who played Jacob's twin brother, the Teen in Black.

"It was really cool, because we both got see lots of the island together," he said. "We went deep into the jungle where the light was. That, I think, was on the eastern or the northern shore [of Hawaii's island of Oahu, where the series shot]. We went into the jungle, and there was just this really brilliant river. Not a lot of people know about it."

Beyond the joy of running around the Lost island set, "I really loved the parts where I got to go so deep into my own emotions. Because that, I think, really, in a sense, helped me as an actor. It took me up to the next level, being able to go that deep," he said.

Lost airs the next-to-last episode tonight; the two-and-a-half-hour series finale airs on Sunday at 9 p.m. on ABC.

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