The 42-year-old actor, who plays William on the HBO series, confirmed at the Television Critics Association winter press tour Tuesday that he will appear in the new season.
"I mean, yeah, I pop in," he told reporters, according to Entertainment Weekly.
The Season 1 finale included the revelation that William is a younger version of the villainous Man in Black (Ed Harris).
Simpson said he hopes the new season will further explore William's past.
"I wish there was exploration between the time when William's heart was broken and we see the result. I want to know how much it takes and how hard he tried not to go there. But I don't write the story," he said, according to TV Guide.
Simpson had promised in an interview with Esquire published Monday that Season 2 will be epic, saying the plot lines have left him awed.
"Everything I hear, I'm like, 'Oh my God," he said.
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