Based on these observations aiming to extend the approach "trigonal 2D carbon  tetrahedral 3D carbon" to "trigonal 3D carbon  tetrahedral 3D carbon" transformations, a novel allotrope BCT-C 20 is proposed herein with dia topology, close to diamond in all its physical properties. The adopted modus operandi goes through merging crystal chemistry manipulations with DFT investigations of the ground state structure energy and the energy derived quantities, particularly those reporting on the mechanical, dynamic, and thermodynamic ones. Agreements with available experimental data of diamond let assign BCT-C 20 the label of "pseudo-diamond".