Digital twins have been a trending concept in recent years. As a result, the number of digital twins has been steadily growing, and their reuse and composition are open questions. For example, The Thing In The Future (Thing'In) platform gives the possibility to represent a complex system as a Property Graph of Digital Twins (DT)s. However, the representation of the graph hinders understanding of the system and raises the question of modeling more complex digital twins and synchronizing the graph with the system it represents. In this paper, we propose an approach for creating Composite Digital Twins (CDT)s of complex systems based on a graph of Digital Twins (DT)s. The approach is articulated between a Data Plane (DP) which hosts the graph representation of a complex system and a Control Plane (CP) that synchronizes the DP and the Physical Plane (PP) hosting the complex system. In our solution, we provide mechanisms to create user-defined CDTs that are a composition of other DTs. We also propose transparent mechanisms to ensure the synchronisation of CDTs with the physical world. We explain the main steps of our approach illustrated by an example and discuss possible use cases. CCS Concepts: • Computer systems organization → Embedded and cyber-physical systems; n-tier architectures; • Theory of computation → Streaming models; •