Evolution of mass of the two components of the binary that forms reported HR 6819 inner-binary-like system in the isolated binary evolution framework. The primary (green line) loses most of its mass during the CE phase (red line) and collapses into a BH at 8.6 Myr after ZAMS. The secondary star (blue line) remains in its MS with almost constant mass for 50 Myr. Then it loses most of its mass during two stable RLOF events (grey lines).