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We present an extensive study of the Sagittarius II (Sgr II) stellar systemusing MegaCam g and i photometry, narrow-band, metallicity-sensitive CalciumH&K doublet photometry, augmented with Keck II/DEIMOS multi-objectspectroscopy. We are able to derive and refine the Sgr II structural andstellar properties: the colour-magnitude diagram implies Sgr II is old (12.0 +-0.5 Gyr) and metal-poor. The CaHK photometry confirms the metal-poor nature ofthe satellite ([Fe/H]CaHK = -2.32 +- 0.04 dex) and suggests that Sgr II hostsmore than one single stellar population ({\sigma} CaHK = 0.11+0.05-0.03 dex).From the deep spectroscopic data, the velocity dispersion of the system isfound to be {\sigma}vr = 2.7+1.3-1.0 km s-1 after excluding two potentialbinary stars. Using the Ca infrared triplet measured from our highestsignal-to-noise spectra, we are able to confirm the metallicity and dispersioninferred from the Pristine photometric metallicities: ([Fe/H] = -2.23 +- 0.05dex, {\sigma}spectro = 0.10+0.06-0.04 dex). Sgr II's metallicity and absolutemagnitude (MV = -5.7 +- 0.1 mag) place the system on the luminosity-metallicityrelation of the Milky Way dwarf galaxies despite its small size. The low, butresolved metallicity and velocity dispersions paint the picture of a slightlydark matter-dominated satellite. Furthermore, using the Gaia Data Release 2, weconstrain the orbit of the satellite and find an apocenter of 118.4+28.4-23.7kpc and a pericenter of 54.8+3.3-6.1 kpc. The orbit of Sgr II is consistentwith the trailing arm of the Sgr stream and indicates that it is possibly asatellite of the Sgr dSph that was tidally stripped from the dwarf's influence.

The Pristine Dwarf-Galaxy survey - II. In-depth observational study of the faint Milky Way satellite Sagittarius II