Trammell explained that his character Sam will have some romantic storylines with new character Luna, played by Janina Gavankar.
"She's a shapeshifter, so I can really connect with her," Trammell told The Wrap. "And she's also very mysterious, and I think Sam is drawn to that.
"She's kind of like Sam in a lot of ways. He was and still is to a certain extent a mysterious character in town... I don't think anybody knows about him killing two people."
Trammell revealed that Sam will also become acquainted with some other characters, saying: "In addition to her I meet these other shapeshifters and there's a real community of shapeshifters. This year we explore the mythology of shapeshifting."
Trammell also admitted that he does not really worry about the nudity on True Blood but explained that the sex scenes can be a problem.
"The sex scenes are really hard and it's not really hard because you have to be naked - that's always sort of a thing," he said. "It's really about the intimacy and creating intimacy with someone you don't necessarily know all that well. That's a tricky thing to pull off... Getting that connection and also doing it in front of a bunch of people."
True Blood returns for its new season on June 26 on HBO.
Watch a trailer for the fourth season of True Blood below: