Stefan was Lorna Bucket's childhood friend in the Gamma Forests. When a spaceship crashed in the forest, a "massive, scaly creature" emerged from the wreck and began chasing Lorna and Stefan. The Eleventh Doctor arrived, telling Lorna to run.
She saw Stefan fallen over and about to be attacked by the creature, so she dragged him out of the way. Stefan tended to his bruises as Lorna chased after the Doctor, who had drawn the creature away from the two. (PROSE: Lorna's Escape)