Detailed insight into the electronic structure of the ground state and the lowest lying excited states of the UD3 defect in 4H and 6H SiC has been obtained. This was achieved by a combination of photoluminescence- (PL), PL excitation- (PLE), polarization- and Zeeman-experiments. It is shown that the low temperature no-phonon (NP) line of LJD3 at 1.3555 eV in 4H SiC and 1.3430 eV in 6H SiC originates from a transition between a doublet excited state and the singlet ground state.