FG Sagittae is a supergiant star in the constellation Sagitta at a distance of 4000 light-years. When first noted in 1943, it was identified to be a variable star, and it was found to be a hot, blue star of stellar spectral type B in 1955. Since then it has expanded and cooled, becoming a yellow G-type star by 1991, and then further cooling to become an orange K-type star. It started to pulsate when becoming an A-type star with a period of 15 days. This period later increased to over 100 days. Since 1992 the star has exhibited fadings and recoveries similar to that of a R Coronae Borealis variable star; this behavior is emphasized by a hydrogen deficiency typical for this class of stars. It has been proposed that this star has undergone a late thermal pulse (LTP) of helium fusion after having left the asymptotic giant branch (AGB) to move towards the hottest end of the "white dwarf cooling track". This thermal pulse is believed to have revived this aged star to once again, for a short time, behave as an AGB star. FG Sagittae is the central star of the planetary nebula Henize 1-5. Observations In 1943, a star designated AN 377.1943 was discovered to be a previously-unknown variable star. It was designated CSV 5066 as a suspected variable, and then FG Sagittae as a confirmed variable star. At the time, its variations were described as being irregular, but it was soon noted that the average brightness was steadily increasing. It brightened by about two magnitudes between 1943 and 1970, and then began to fade. Examination of old photographic observations found that the star had been brightening since at least 1900, with extrapolations suggesting that the minimum had occurred around 1880. As it faded, FG Sagittae began to show periodic variations, at first a period of 80 days, but increasing to 130 days. In 1992, the periodic variations ceased and the brightness decreased by five magnitudes in only two months. Since then, it has continued to show occasional deep fading events, appearing much like an R Coronae Borealis star. The spectrum of FG Sagittae when it was first noted as a variable star was that of a blue supergiant. The first reliable spectral class is B0 in 1930. Extrapolation of the brightness and colour indices suggest it may have been an O3 star in 1890. It