A vehicle having a vehicle body including a front portion, an opposing rear end portion and an underbody portion configured to face a road surface; and an active diffuser assembly disposed on the underbody portion and configured to control ambient airflow passing under the vehicle body. The active diffuser assembly includes a fixed panel disposed on the vehicle underbody; a movable active panel disposed adjacent the fixed panel and configured for selective movement to be deployed away from the vehicle body and to be retracted toward the vehicle body for stowage; and an actuator configured to deploy and retract the movable active panel, the fixed panel and the movable active panel defining a continuous plane when the movable panel is in the stowed position.