We present a photometric and spectroscopic study of the unique isolated nearby dSph galaxy KKR25 .
The galaxy was resolved into stars with HST/WFPC2 including old red giant branch and red clump .
We have constructed a model of the resolved stellar populations and measured the star formation rate and metallicity as function of time .
The main star formation activity period occurred about 12.6 to 13.7 Gyr ago .
These stars are mostly metal-poor , with a mean metallicity \mbox { [ Fe / H ] } \sim - 1 to -1.6 dex .
About 60 per cent of the total stellar mass was formed during this event .
There are indications of intermediate age star formation in KKR25 between 1 and 4 Gyr with no significant signs of metal enrichment for these stars .
Long-slit spectroscopy was carried out using the Russian 6-m telescope of the integrated starlight and bright individual objects in the galaxy .
We have discovered a planetary nebula ( PN ) in KKR25 .
This is the first known PN in a dwarf spheroidal galaxy outside the Local Group .
We have measured its oxygen abundance 12 + \log ( \textrm { O / H } ) = 7.60 \pm 0.07 dex and a radial velocity V _ { h } = -79 km s ^ { -1 } .
We have analysed the stellar density distribution in the galaxy body .
The galaxy has an exponential surface brightness profile with a central light depression .
We discuss the evolutionary status of KKR25 , which belongs to a rare class of very isolated dwarf galaxies with spheroidal morphology .