[en] The access to the so-called 'monster sawteeth regime during additional heating in JET is related to the creation of energetic trapped ions inside the plasma. Several models have been put forward to explain the behaviour of the central part of the discharge. These studies mainly analyse the influence of the fast ion population on the ideal internal kink mode destabilized by the thermal pressure gradient. However, the stability of the associated reconnecting mode is to be considered. Along this line, in this paper, we investigate a new stabilization criterion expressing that the fast trapped ions (by balancing the effect of the current density gradient) provide a negative Δ' to that mode. (author) 5 refs., 3 figs