Evolution of orbital and stellar parameters of V4142 Sgr. Left: schematic behavior of radius and mass for both stars. While the two stars evolve separately, the donor star (black line) expands to fill the RL, and the initial radius of the gainer star (dashed red line) increases and later decreases during the rejuvenation. Center: evolution of the orbital period as a function of the mass of the primary star (donor) for V4142 Sgr. Right: theoretical orbital velocity curve for both components as a function of their masses. The orbital velocity of the primary component (black line) increases during the mass-loss process, known as spin-up, and later decreases, reaching the current value. The RV of the companion (i.e., gainer) star (dashed red line) decreases, and its mass increases.