The duo have recently started working together more but Somerhalder told MTV that they will soon start to disagree.
"I know Damon and Stefan are battling some really cool supernatural forces," he said. "But Damon and Stefan also are starting to butt heads again and start to bicker again."
He added: "That's what I think is a lot of fun about the show. As much as I love Paul Wesley [who plays Stefan] and we're bros off screen, it's great when we're battling on screen."
Somerhalder also suggested that original vampire Klaus will have a big impact when he arrives on the show, saying: "I think everyone's on their toes now more. Because he's a badass."
The Vampire Diaries returns for a new episode on April 7 at 8/7c on The CW.