  Since its launch, the X-ray and gamma-ray observatory INTEGRAL satellite has
revealed a new class of high-mass X-ray binaries (HMXB) displaying fast flares
and hosting supergiant companion stars. Optical and infrared (OIR) observations
in a multi-wavelength context are essential to understand the nature and
evolution of these newly discovered celestial objects. The goal of this
multiwavelength study (from ultraviolet to infrared) is to characterise the
properties of IGR J16465-4507, to confirm its HMXB nature and that it hosts a
supergiant star. We analysed all OIR, photometric and spectroscopic
observations taken on this source, carried out at ESO facilities. Using
spectroscopic data, we constrained the spectral type of the companion star
between B0.5 and B1 Ib, settling the debate on the true nature of this source.
We measured a high rotation velocity of v = 320 +/- 8 km/s from fitting
absorption and emission lines in a stellar spectral model. We then built a
spectral energy distribution from photometric observations to evaluate the
origin of the different components radiating at each energy range. We finally
show that, having accurately determined the spectral type of the early-B
supergiant in IGR J16465-4507, we firmly support its classification as an
intermediate supergiant fast X-ray transient (SFXT).
