  Using an elegant model involving only $\Gamma_{6c}$ and $\Gamma_{8v}$ bands,
massless Kane fermions were defined as the particles associated with the
peculiar band structure of gapless HgCdTe crystals. Although their dispersion
relation resembles that of a pseudo-spin-1 Dirac semimetal, these particles
were originally considered to be hybrids of pseudospin-1 and -1/2 fermions.
Here we unequivocally find that by considering an additional $\Gamma_{7c}$
conduction band inherent in HgCdTe crystals, the Kane fermions are ultimately
two nested Dirac particles. This observation allows the direct application of
Lorentz transformations to describe the relativistic behavior of these
particles in crossed electric and magnetic fields. By studying the relativistic
collapse of their Landau levels at different orientations between the crossed
fields and the main crystallographic axes, we demonstrate that the Kane
fermions strikingly decay into two independent Dirac particles with increasing
of electric field. Our results provide new insight into semi-relativistic
effects in narrow-gap semiconductors in crossed electric and magnetic fields.
