We investigate room-temperature structural properties and spontaneous magnetism in a series of Hg1-xFexSe (0.00012 ≤ x ≤ 0.0013) diluted magnetic semiconductor bulk single crystals grown by the Bridgman method. In order to elucidate the experimentally observed high-temperature magnetism in the studied systems, the dependencies of magnetization on magnetic field strength for the entire sample series were studied. Their detailed analysis revealed impurity contributions typical of ferromagnetic materials, which are described by magnetization curves with the parameters characterizing the spontaneous spin magnetism of the donor conduction electrons of the outer d-shells of the impurity atoms. According to the previously-developed theoretical concept, such a magnetic ordering mechanism stems from the direct exchange coupling of donor conduction electrons due to hybridization of impurity states, rather than from inter-impurity interactions. The results of optical emission spectroscopy and X-ray diffraction analysis confirmed the observed ferromagnetism to be intrinsic and linked directly to the d-electrons of iron impurity atoms.