Siblings of individuals with developmental disorders often assume increased care responsibilities, from an early age. Taking on this role can have long-term consequences for their psychosocial development, family relationships and, overall quality of life. Despite their crucial role in the family system, their voices often remain unheard both in research and practice. The aim of this study was to explore in depth the lived experiences of adult siblings who grew up with a brother or sister with a developmental disorder, focusing on their caregiving role, the quality of sibling relationships and the psychological impact of this experience. To this end, 5 semi-structured interviews were conducted and the method of thematic analysis was used in order to identify themes and patterns. The analysis revealed five key themes: 1) caregiving role and responsibilities, 2) the "invisible child" within the family, 3) guilt and anxiety about the future, 4) social networks and need for support and, 5) positive aspects of the experience. The findings underline the need for further research on the topic in order for targeted psychosocial support services and interventions to be designed and implemented By amplifying the voices of this often overlooked population, this research advocates for greater inclusion of the siblings' perspective in policy making and clinical practice concerning developmental disabilities.