  The spectroscopic evolution of Hen\,3-1357, the Stingray Nebula, is presented
by analysing data from 1990 to 2021. High resolution data obtained in 2021 with
South African Large Telescope High Resolution Spectrograph and in 2009 with
European Southern Observatory-Very Large Telescope UVES spectrograph are used
to determine physical conditions and chemical abundances in the nebula. From
comparison of these data with data from different epochs it is found that the
intensity of highly-ionized emission lines has been decreasing with time, while
the emission of low-ionization lines has been increasing, confirming that the
nebula is recombining, lowering its excitation class, as a consequence of the
changes in the central star which in 2002 had an effective temperature of
60,000 K and from then it has been getting colder. The present effective
temperature of the central star is about 40,000 K. It has been suggested that
the central star has suffered a late thermal pulse and it is returning to the
AGB phase. The nebular chemistry of Hen\,3-1357 indicates that all the
elements, except He and Ne, present sub solar abundances. The comparison of the
nebular abundances with the values predicted by stellar nucleosynthesis models
at the end of the AGB phase, shows that the central star had an initial mass
lower than 1.5 M$_{\odot}$. We estimated the ADF(O$^{+2}$) to be between 2.6
and 3.5.
