  We report the discovery of two new giant radio galaxies (GRGs) using the
MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) survey.
Both GRGs were found within a 1 deg^2 region inside the COSMOS field. They have
redshifts of z=0.1656 and z=0.3363 and physical sizes of 2.4Mpc and 2.0Mpc,
respectively. Only the cores of these GRGs were clearly visible in previous
high resolution VLA observations, since the diffuse emission of the lobes was
resolved out. However, the excellent sensitivity and uv coverage of the new
MeerKAT telescope allowed this diffuse emission to be detected. The GRGs occupy
a unpopulated region of radio power - size parameter space. Based on a recent
estimate of the GRG number density, the probability of finding two or more GRGs
with such large sizes at z<0.4 in a ~1deg^2 field is only 2.7x10^-6, assuming
Poisson statistics. This supports the hypothesis that the prevalence of GRGs
has been significantly underestimated in the past due to limited sensitivity to
low surface brightness emission. The two GRGs presented here may be the first
of a new population to be revealed through surveys like MIGHTEE which provide
exquisite sensitivity to diffuse, extended emission.
