Grandpa Cecil becomes Sebastian's primary guardian, raising the orphaned infant alongside his biological granddaughter, Anne-Marie, in a Pyrenees mountain village. He provides a stable home despite community bullying directed at Sebastian due to his unknown parentage.

An elderly man possessing deep knowledge of mountain survival and wilderness skills, Cecil mentors Sebastian, imparting essential outdoor abilities like navigation and resourcefulness for the harsh alpine terrain. This guidance forms a crucial foundation for Sebastian's later journey.

Cecil demonstrates a patient and nurturing parenting approach, contrasting with Anne-Marie's stricter methods. He openly disapproves of her harshness towards Sebastian, particularly regarding the boy's longing for his birth mother, which creates occasional family tension. Cecil consistently prioritizes Sebastian's emotional well-being and fosters his curiosity about the natural world.

When Sebastian flees the village with the dog Belle to evade authorities seeking to euthanize her, Cecil faces a moral conflict between his protective instincts and respect for the boy's independence. Though deeply concerned for Sebastian's safety, he ultimately does not forcibly prevent the departure, acknowledging the profound bond between child and dog.

Following Sebastian's departure, Cecil remains a background presence, the narrative implying his ongoing concern for the boy's welfare during the journey. His role shifts to that of a supportive figure awaiting Sebastian's potential return, anchoring the stable home life Sebastian may revisit after his quest.