Left panel: Mass-radius relation with PAIR-2 highlighted. The dots correspond to the mass and radius values given by our models at 10, 20, 30, 40, and 50 kK, while squares represent other possible values (at 20 and 30 kK) if the WD is not on the final cooling track. Right panel: Radius of the donor star as a function of the effective temperature for PAIR-2. Dashed lines represent fast parts of the tracks. The dots correspond to remnants on the final cooling track, while squares show other possible radii that could be observed for the same object at 20 and 30 kK.