Abstract:The main novel part of the paper is to identify the 16 extra bosonic dimensions of the Heterotic string theory with the negative signature of K3 Kähler manifold and these in turn are the source of pure dark energy. Guided by the basic ideas and structure of heterotic string theory we establish an energy density triality, which add together to the theoretically expected energy density based on Einstein's relativity. Thus Einstein's famous formula E = mc 2 is found in integer approximation to be the sum of three sectors, namely 2 1 5 16 22is the ordinary energy density,is the dark matter energy density andis the pure dark energy density where m is the mass, c is the velocity of light and 16 is the number of heterotic strings extra bosons. We demonstrate further that strictly speaking dark matter is weakly coupled with pure dark energy and that while dark matter and ordinary energy are attracting in the conventional way, pure dark energy has an opposite sign similar to the extra 16 dimensions of heterotic strings making it act effectively in the opposite direction in conformity with the negative sign and magnitude of the corresponding K3 Kähler manifold.