Evolutionary track of the 2.6 M_⊙ star (the white dwarf progenitor) from two MESA simulations. Left: Pre-common envelope evolution, starting at the zero-age main sequence, followed by the onset and termination of stable mass transfer, and culminating in the initiation of the common envelope phase (this corresponds to the same simulation as Figure 1). Right: The white dwarf cooling track was simulated by removing the red giant envelope. The system then emerges as a compact binary, the secondary contracts to form a white dwarf, and the track continues until it reaches the present-day configuration of PTF J2238+7430, marked with a yellow star. In both panels, the color bar indicates the change in the mass of the white dwarf progenitor.