The AMC show's creator was reflecting on the latest episode to air in the US, which focused on the death of Shane (Jon Bernthal).
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"We knew that [Shane] was going to die before we cast Jon Bernthal," Kirkman told The Hollywood Reporter. "If the first season had been 13 episodes instead of six, Shane's story would have been told all in that first season; it would have been much like the comic book where Shane dies at the end of the first volume.
"We knew from day one when we sat down in the writers' room to pull out the second season that this was going to be the season that Shane died. It was always about working toward that and building up that character and setting up this confrontation between Rick and Shane."
Kirkman further explained that a key question about Shane's death - why the character came back to life as a zombie without apparently having been bitten - will be explained soon.
"[It's] something that we connected through the Jenner whisper secret and is something that is going to be revealed in the next episode," he said.
The Walking Dead's second season concludes next Sunday (March 18) at 9/8c on AMC.
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