  We present the discovery of a transiting massive giant planet around
TOI-4603, a sub-giant F-type star from NASA's Transiting Exoplanet Survey
Satellite (TESS). The newly discovered planet has a radius of
$1.042^{+0.038}_{-0.035}$ $R_{J}$, and an orbital period of
$7.24599^{+0.00022}_{-0.00021}$ days. Using radial velocity measurements with
the PARAS {and TRES} spectrographs, we determined the planet's mass to be
$12.89^{+0.58}_{-0.57}$ $M_{J}$, resulting in a bulk density of
$14.1^{+1.7}_{-1.6}$ g ${cm^{-3}}$. This makes it one of the few massive giant
planets with extreme density and lies in the transition mass region of massive
giant planets and low-mass brown dwarfs, an important addition to the
population of less than five objects in this mass range. The eccentricity of
$0.325\pm0.020$ and an orbital separation of $0.0888\pm0.0010$ AU from its host
star suggest that the planet is likely undergoing high eccentricity tidal (HET)
migration. We find a fraction of heavy elements of $0.13^{+0.05}_{-0.06}$ and
metal enrichment of the planet ($Z_{P}/Z_{star}$) of $4.2^{+1.6}_{-2.0}$.
Detection of such systems will offer us to gain valuable insights into the
governing mechanisms of massive planets and improve our understanding of their
dominant formation and migration mechanisms.
