Stellar populations in a Milky Way/M31-like galaxy from TNG50 (ID_{z = 0} = 411449). Top: age distributions of disk stars (gray) and in situ halo stars (red), defined as in situ stars with L_z ≥ 500 and <500 kpc km s⁻¹, respectively. The vertical lines mark the merger times of two satellites with stellar mass ratios of 0.45 (blue) and 0.06 (green). Bottom: galactocentric distances of accreted stars as a function of lookback time.