We demonstrate local coherent heteroepitaxial growth of silicon carbide (SiC) on diamond, a result contrary to current understanding of heterojunctions as the lattice mismatch exceeds 20%. High-resolution transmission electron microscopy confirms the quality and atomic structure near the interface. Guided by molecular dynamics simulations, a theoretical model is proposed for the interface which alleviates the large lattice strain via point dislocations in a two-dimensional plane without forming extended defects in three dimensions. The possibility of realising heterojunctions of technologically