  We report the discovery of K2-31b, the first confirmed transiting hot Jupiter
detected by the K2 space mission. We combined K2 photometry with FastCam lucky
imaging and FIES and HARPS high-resolution spectroscopy to confirm the
planetary nature of the transiting object and derived the system parameters.
K2-31b is a 1.8-Jupiter-mass planet on an 1.26-day-orbit around a G7\,V star
($M_\star=0.91$~\Msun, $R_\star=0.78$~\Rsun). The planetary radius is poorly
constrained (0.7$<$$R_\mathrm{p}$$<$1.4~\Rjup), owing to the grazing transit
and the low sampling rate of the K2 photometry.
