The process of formation of core−shell nanocrystals, using a reverse micellar system, has been modeled using the Monte Carlo technique, and the post-core route for the formation of core−shell nanocrystals has been studied. The model is divided into two parts: (a) the formation of core nanoparticles and their subsequent growth due to coagulation, and (b) the formation of the shell via the ion-displacement mechanism. The model for core nanoparticle formation and subsequent growth includes the phenomena of finite nucleation, growth via intermicellar exchange, and coagulation of nanoparticles after their formation. The growth of the core is taken to be limited by the size of the micellar core. The model explains the possible mechanism of core−shell nanocrystal formation. The simulation results compare well with those observed experimentally.