 Complete the following phrase:  He starred in the 2011 horror feature Shark Night 3D. Walls played a guest role on the second season of the ABC fantasy series Once Upon a Time, as Sir Lancelot. He returned to the show during the fifth season as a guest star. He played the role of Shawn in the TV series Power. On August 1, 2017, Walls was cast in Clint Eastwoods biopic , about the thwarted 