Digital Twins (DT) represent a strategic enabler for the next generation of cyber-physical applications in multiple challenging use cases. Existing software approaches are mostly conceived to vertically adhere to domain- and application-specific constraints, hence designed through a monolithic vision tightly coupling DTs to the physical assets and applications at hand. This limits flexibility in terms of deployment, scalability, and adaptability to different domains. In this paper, we introduce an architectural blueprint and implementation for an event-driven notion of DT, meant to tackle such limitations by promoting flexibility and decoupling. As conceptual validation, we present its application to the challenging context of healthcare emergency missions management.