  The photometric evolution of M31-RV has been investigated on 1447 plates of
the Andromeda galaxy obtained over half a century with the Asiago telescopes.
M31-RV is a gigantic stellar explosion that occurred during 1988 in the Bulge
of M31 and that was characterized by the appearance for a few months of an M
supergiant reaching M_bol=-10. The 1988 outburst has been positively detected
on Asiago plates, and it has been the only such event recorded over the period
covered by the plates (1942-1993). In particular, an alleged previous outburst
in 1967 (Sharov 1990, SvAL, 16, 199) is excluded by the more numerous and
deeper Asiago plates, with relevant implication for the interpretative models
of this unique event. We outline a close analogy in spectral and photometric
evolution with those of V838 Mon which exploded in our Galaxy in 2002. The
analogy is found to extend also to the closely similar absolute magnitude at
the time of the sudden drop in photospheric temperature that both M31-RV and
V838 Mon exhibited. These similarities, in spite of the greatly differing
metallicity, age and mass of the two objects, suggest that the same, universal
and not yet identified process was at work in both cases.
