In this paper the author argues that sibling relationships are a missing piece of the eating disorder puzzle. She notes that disturbing relationships with siblings have been present all along in the literature, but have not been included as a separate area of study. They have thus been hiding in plain sight, present but not accounted for in our psychoanalytic theories. Without an adequately developed place for sibling relationships in our theories, an essential layer of understanding is missed and the impact on the psyche remains entrenched. The author offers two clinical vignettes to illustrate how eating disorder patients' internal and external sibling relationships contribute to the cruel superegos and destructive narcissism that are central features of these disorders.