We report the discovery of a planet in the microlensing event OGLE-2018-BLG-1269, with planet-host mass ratio $q sim 6times10^{-4}$, i.e., $0.6$ times smaller than the Jupiter/Sun mass ratio. Combined with the $Gaia$ parallax and proper motion, a strong one-dimensional constraint on the microlens parallax vector allows us to significantly reduce the uncertainties of lens physical parameters. A Bayesian analysis that ignores any information about light from the host yields that the planet is a cold giant $(M_{2} = 0.69_{-0.22}^{+0.44},M_{rm J})$ orbiting a Sun-like star $(M_{1} = 1.13_{-0.35}^{+0.72},M_{odot})$ at a distance of $D_{rm L} = 2.56_{-0.62}^{+0.92},{rm kpc}$. The projected planet-host separation is $a_{perp} = 4.61_{-1.17}^{+1.70},{rm au}$. Using {it Gaia} astrometry, we show that the blended light lies $lesssim 12,$mas from the host and therefore must be either the host star or a stellar companion to the host. An isochrone analysis favors the former possibility at $>99.6%$. The host is therefore a subgiant. For host metallicities in the range of $0.0 leq {rm [Fe/H]} leq +0.3$, the host and planet masses are then in the range of $1.16 leq M_{1}/M_{odot} leq 1.38$ and $0.74 leq M_{2}/M_{rm J} leq 0.89$, respectively. Low host metallicities are excluded. The brightness and proximity of the lens make the event a strong candidate for spectroscopic followup both to test the microlensing solution and to further characterize the system.
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