We have presented a model of two consecutive pairs of triplet excitons, which consists of a succession of two pairs known as short pair and long pair with reference to their respective lifetimes. We have applied this model to the modulation of prompt fluorescence (PF) in crystalline tetracene by a static magnetic field (MFE) and a microwave field (F-ODMR). The two types of experiments have been enough perfectly reproduced by using the same set of kinetics constants. Thus, we have arrived to rise the inconsistencies which one reproached the Seventies kinetic model.