Radio frequency heating of majority ions is of prime importance for understanding the basic role of auxiliary heating in the activated D-T phase of ITER. Majority Deuterium Ion-Cyclotron Resonance Heating (ICRH) experiments at the fundamental cyclotron frequency were performed in JET. In spite of the poor antenna coupling at the lowest possible commissioned RF frequency (25MHz), this heating scheme proved promising when adopted in combination with D Neutral Beam Injection (NBI). The experiments were performed in a ~90% D, 5% H plasma with some pulses including traces of Be and Ar. Up to 2MW of ICRH power was applied with dipole phasing in conjunction to ~6MW of NBI power, either using 80keV “normal” beam or 130keV “tangential” beam injection. The toroidal magnetic field strength was typically Bo=3.3T, providing core ICRH of the bulk D ions. The effect of fundamental D ICRH was clearly demonstrated in these experiments: By adding ~25% of heating power (PICRH = 1.7MW / PNBI+OH = 7MW) the fusion power was increased up to 30-50%, depending on the type of NBI adopted. At this power level, the ion and electron temperatures increased from Ti ~ 4.0keV and Te ~ 4.5keV (NBI-only phase) to Ti~5.5keV and Te~5.2keV (ICRH+NBI phase), respectively. The increase in the neutron yield was stronger when 80keV rather than 130keV Deuterons were injected in the plasma. It is shown that the neutron rate, the diamagnetic energy and the electron as well as ion temperature scale roughly linearly with the applied RF power. A synergistic effect of the combined use of ICRF and NBI heating was observed: (i) The number of neutron counts measured by the neutron camera during the combined ICRF+NBI phases of the discharges exceeded the sum of the individual counts of the NBI-only and ICRF-only phases; (ii) A substantial increase in the number of slowing-down beam ions was detected by the TOFOR spectrometer when ICRF power was switched-on; (iii) A small D subpopulation with energies slightly above the NBI launch energy were detected by the neutral particle analyzer and g-ray spectroscopy.