Notes. For the pre-CE and post-CE evolution, we used the MESA code with the assumptions described in Sect. 3. For the CE evolution, we computed the post-CE orbital period using Eqs. (1) and (2), assuming α_CE = 0.3 and α_CE ≈ 0.82. The terms M₁ and M₂ and Type₁ and Type₂ are the masses and stellar types of the primary and secondary, respectively. P_orb is the orbital period and the last column corresponds to the event occurring to the binary at the given time in the first column. The row in which the binary has the present-day properties of FN Sgr is highlighted in boldface. For the WD evolution, we interpolated the evolutionary sequences calculated by Bédard et al. (2020) to estimate the mass fraction of the crystallized matter. We assumed a magnetic field diffusion timescale of ∼600 Myr and that the amount of angular momentum accreted by the WD before the binary became a SySt was enough to spin up the WD towards the super-equipartition regime. Abbreviations: MS (main sequence star), SG (subgiant star), FGB (first giant branch star), CHeB (core helium burning), E-AGB (early asymptotic giant branch star), TP-AGB (thermally-pulsing asymptotic giant branch star), WD (white dwarf), RLOF (Roche lobe overflow), CE (common envelope), SySt (symbiotic star).