Left panel: Median [Fe/H] of the accreted part of the stellar halo along the semi-minor axis as a function of the accreted stellar halo mass of each galaxy. Some observed MW-mass galaxies taken from GHOSTS data are also shown as green triangles, as well as the MW-mass set of Auriga simulations represented with squares. All simulated galaxies are colour-coded according to their total DM mass. We find a strong correlation between the [Fe/H] and the stellar mass of accreted stellar halo. The arrow represents the Auriga 15 that does not have accreted material in the direction of the semi-minor axis of its stellar halo. Right panel: Median [Fe/H] of the accreted stellar halo as a function of the stellar mass provided to the whole galaxy by the most dominant satellite of the accreted stellar halo. All galaxies are colour-coded by their total accreted stellar mass.