Check out the official synopsis of the season premiere of Supernatural, airing September 24! It's a year after last season's finale, Sam goes to Dean to get him back into hunting, and Grandpa Campbell is indeed back, although we don't yet know how. I can't wait to see it!
MITCH PILEGGI (“X-Files,” “Sons of Anarchy”) RETURNS AS DEAN AND SAM’S GRANDFATHER — It’s a year later and Dean (Jensen Ackles) has given up hunting and is living with Lisa (guest star Cindy Sampson) and her son Ben (guest star Nicholas Elia). Mysteriously freed from his cage in hell, Sam (Jared Padalecki) finds Dean and tells him he needs to rejoin the fight and introduces Dean to a world—a family—he never even knew existed.... the Campbells, his mother’s family, lead by none other than their Grandfather Samuel (Pileggi). Phil Sgrricia directed the episode written by Sera Gamble (#601).
Source: The CW