Hertzsprung–Russell diagram of both stars in the binary. The black line corresponds to the WD progenitor, that is, the initially more massive star, up to the onset of CE evolution (red solar symbol). During pre-CE evolution, the initially less massive star, which is the RG progenitor (represented by the green lines) evolved only slightly. After CE evolution (dot-dashed line), the companion evolved, became an evolved RG and quickly afterward its atmosphere filled its Roche lobe. At this moment the binary became a SySt and, shortly after that (red pentagon), its properties were similar to those of FN Sgr.