FG Sge is one of the most unique variable stars known.  Evolving as we watch, it's variations are totally unpredictable. Before 1992,  FG Sge spent many years as a magnitude 9 star before major 'dust' events began in mid 1992.  The star has also evolved and cooled from a B type star to it's present type K2 in just over a century.   It's the central star of the Planetary Nebula PK060.3-07.3.  

As a post AGB star, it's likely that FG Sge has undergone a Late Thermal Pulse which has probably revived it's AGMB status, and speculation as to whether FG Sge becomes hydrogen deficient in the future continues.  Last recording of the star was in 2008 at just below magnitude 17.0C. Recent data indicate the star remains at 18-19th magnitude.