Implementing Circular Economy principles in the built environment is of utmost importance to reduce raw material extraction and generated waste. A transition is essential, especially as it is responsible for about 40% - 60% of global raw material extraction and 33% of total waste in the European Union. This paper shows the methodological approach to generate a digital Building model to enable Circular Economy in the early design stage. In addition to Generative Design methods, which enable an automated variant generation of Digital building models, coupled to a BIM object database, algorithms to assess the environmental Impact are also implemented to enable an evaluation of the circularity, and sustainability of the building design. By visualizing the assessments of the generated variants of (so-called) Circular Twins in a Virtual Reality environment, including user interaction with a voice-controlled virtual Agent, the digital Circular Twin ecosystem enables the early implementation of the goals of the circular economy and sustainability in Architecture, Engineering and Construction.