  We report the discovery of a planetary nebula centered on the poorly studied
symbiotic binary star DT Ser. In a few other symbiotic stars spatially resolved
nebulae have been discovered: however, only one of them might be a genuine
planetary nebula, while the others are likely to originate in complex mass
ejections episodes from the interacting binary central stars, possibly related
to nova-like outbursts. The rim of the planetary nebula around DT Ser is
severely distorted toward a brighter star, 5 arcsec away. In infrared WISE
data, this star shows the presence of a detached cold dust shell such as those
observed in post-AGB stars. The apparent association of the symbiotic star and
its planetary nebula with the nearby possible post-AGB object is discussed. We
also discuss the sparse and conflicting literature data that could support an
observed variability of the surface brightness of the planetary nebula. The
puzzling and intriguing characteristics displayed by DT Ser are surely worth
further and more detailed investigations.
