Movement of tidal tail (star particles in blue and gas particles in grey) from M31 merger model 288 towards the MW and formation of TDG within the tail. Panel a: Tidal tail formed during the second passage of M31 merger with some zones of over-density. Panel b: Particles of the tidal tail that are close to the M31 fall back and form stellar loops that ultimately form the GSS. Panels b and c: Distant parts of the tail escape M31, which then expand moving towards the MW. The formation of at least one TDG and potentially a few more in the dense zone can also be identified. In this coordinate system, the M31 centre (green) is fixed at (0, 0, 0), and the MW is at 0 Gyr is on the z-axis. The stars and gas particles are shown in log-normal density to identify the over-dense regions. The position of the MW (red dot) is calculated for a radial approach between the two galaxies taken as the point mass for the MW mass of model B and the M31 mass from Hammer et al. (2025). The MW’s gravitational impact on the particles is not considered.