Speaking to Entertainment Weekly, David Marshall Grant explained that working as a medic in Afghanistan will have had a big impact on Justin (Dave Annable).
"Justin returns from Afghanistan a very different Justin," he said. "We all felt that it was time for him to grow up."
Grant continued: "He becomes a much more strong and a much more helpful force in the Walker family. I don't think Justin is going to be the problem anymore as much as he might be the solution."
Brothers & Sisters returns for a new season on Sunday at 10/9c on ABC.