Duncan Barrie is the son of Domhnall Barrie and Mackenzie Barrie and the younger brother of Ava Barrie.

A small boy, also blond, stood right behind [Ava].... “This is my brother, Duncan,” she added, looking down at the short boy standing by her. I waved at Duncan, and he backed up behind his older sister’s legs. Maybe shyness was a family thing.

– Dark Waters