In the present paper a new tetragonal equiatomic boron carbonitride is proposed from crystal chemistry rationale and ab initio calculations within DFT . The proposed BCN structure is identified with higher symmetry than monoclinic BCN , and a local tetrahedral configuration favoring BC2N2 tetrahedra over NB2C2 ones. Tetragonal BCN is found cohesive and characterized as mechanically and dynamically stable, with exceptional hardness properties.