General theorem providing a mathematical basis for a grand Unified Field Theory (GUT) is presented. The proof of the theorem is shown to be a recent work entitled 'Generalised Mathematical Proof of Einstein's Theory Using a New Group Theory', which has been reviewed by the American Mathematical Society. This work provides generic solutions to the unified field, from which both the Newtonian and Einsteinian gravitational fields seem to be recoverable. Furthermore, the electromagnetic field seems to be recoverable also from these solutions. Since the investigation does not assume the existence of particles a priori, matter could therefore be interpreted as high field intensity. Therefore, nuclear force fields (strong and weak) seem to be included. The solution seems to mathematically represent the modification of space-time predicted by Einstein's general relativity theory.