In JET-ILW, beam-target reactions contribute to a large fraction of the fusion power generated in deuterium-tritium (D-T) plasmas, with core ion temperatures of 10-12 keV and large neutral-beam injection (NBI) power. Previous modelling done in preparation for the recent D-T campaigns in JET have shown that injecting D beam ions with energies of similar to 120 keV in T-rich plasmas produces larger 14 MeV fusion yield than in 50:50 D:T plasmas, but such scenario had never been tested in past D-T experiments. In addition, the simulations showed that fundamental ion cyclotron resonance heating (ICRH) of the D ions can significantly boost the net fusion reactivity, since both the D-bulk ions and the fast D-beam ions are accelerated to energy ranges that are optimal for the D-T reactions to take place. In the last JET D-T campaigns (DTE2 and DTE3), dedicated experiments confirmed-for the first time-the improved fusion performance of T-rich plasmas with high D-NBI power and highlighted the key impact of fundamental D ICRH on the fusion performance. This new scenario led to the world-wide D-T fusion energy record ever achieved in a fusion device and allowed to sustain more than 12 MW of fusion power averaged over 5 s. The main results of these unprecedented experiments will be presented and the NBI + ICRF physics responsible for the high fusion performance achieved will be highlighted through numerical modelling.