Evolution history of TNG50 501208 (left) and TNG50 546474 (right). We describe the four panels with TNG50 501208. Top : assembly history of the galaxy. The solid thick curves represent two of the most massive mergers the galaxy experienced. The dashed curves represent small mergers. TNG50 501208 has assembled 80% of its DM mass and 72% of its stellar mass at t = 6 Gyr ago. Second row : distance of the satellite to the galacetic center as a function of time. The solid black curve is a major merger ended at t ~ 8.5 Gyr ago. The red curve is the following most massive minor merger with Mmax = 7.1 × 10¹⁰ M_⊙. The vertical dashed red line indicates the time at which it reached the pericenter for the first time. Third row : variation in the disc spin direction as a function of time. The disc was co-aligned with the long-intermediate axis plane of the DM halo at t ~ 6 Gyr ago, and it has tilted 80° in the past 6 Gyr. Bottom: evolution of the DM axis ratios, with p_DM = Y/X and q_DM = Z/X. The DM shape remain largely unchanged in the past 8 Gyr. The four panels in the right show a similar evolution history of TNG50 546474.