  We report the discovery of a hot Jupiter on a 3.28-day orbit around a 1.08
M$_{Sun}$ G0 star that is the secondary component in a loose binary system.
Based on follow-up radial velocity observations of TOI-858 B with CORALIE on
the Swiss 1.2 m telescope and CHIRON on the 1.5 m telescope at the Cerro Tololo
Inter-American Observatory (CTIO), we measured the planet mass to be $1.10\pm
0.08$ M$_{J}$ . Two transits were further observed with CORALIE to determine
the alignment of TOI-858 B b with respect to its host star. Analysis of the
Rossiter-McLaughlin signal from the planet shows that the sky-projected
obliquity is $\lambda = 99.3\pm 3.8$. Numerical simulations show that the
neighbour star TOI-858 A is too distant to have trapped the planet in a
Kozai-Lidov resonance, suggesting a different dynamical evolution or a
primordial origin to explain this misalignment. The 1.15 Msun primary F9 star
of the system (TYC 8501-01597-1, at $\rho$ ~11") was also observed with CORALIE
in order to provide upper limits for the presence of a planetary companion
orbiting that star.
