Spatial and CMD locations of stars and quasars around M31. Left-hand panel: quasars from the Gaia CRF3 (in grey) and added by the latest Gaia catalogue of extra-galactic objects (in black) centred on M31. Middle panel: final blue and red samples of M31 stars superimposed on the central ellipse representing the geometrical cut made on M31. Each quadrant depicted by dashed lines contains the same number of blue stars and the hatched region is used to estimate the properties of the contamination. Right-hand panel: CMD of all the objects from the previous panels.