Kostjasyn, who grew up on the Central Coast before a stint in Melbourne, returns to the club he played 32-games for after his debut in 2010.
“I’m looking forward to getting to the club and seeing all of the young guys tear in and improve on what they’ve built this year,” Kostjasyn said in a statement released by the Knights.
“It’s an exciting time and there’s going to be some hard work.
“It’s been seven years since I’ve lived close to family and friends, so I’m looking forward to coming back.”