  We present and discuss accurate and densely mapped BVRI lightcurves of the
neon Nova Mon 2012, supplemented by the evolution in Stromgren b and y bands
and in the integrated flux of relevant emission lines. Our monitoring started
with the optical discovery of the nova and extend to day +270, well past the
end of the super-soft phase in X-rays. The nova displayed very smoothly
evolving lightcurves. A bifurcation between y and V light-curves took place at
the start of the SSS phase, and a knee developed toward the end of the SSS
phase. The apparent magnitude of the nova at the unobserved optical maximum is
constrained to +2.8=<V=<4.2. The appearance, grow in amplitude and then demise
of a 0.29585 (+/-0.00002) days orbital modulation of the optical brightness was
followed along the nova evolution. The observed modulation has a
near-sinusoidal shape and a weak secondary minimum at phase 0.5. We favor an
interpretation in terms of super-imposed ellipsoidal distortion of the Roche
lobe filling companion and irradiation of its side facing the WD. Similar
lightcurves are typical of symbiotic stars where a Roche lobe filling giant is
irradiated by a very hot WD. Given the high orbital inclination, mutual
occultation between the donor star and the accretion disk could contribute to
the observed modulation. The optical+infrared spectral energy distribution of
Nova Mon 2012 during the quiescence preceeding the outburst is nicely fitted by
a early K-type main-sequence star (~K3V) at 1.5 kpc distance, reddened by
E(B-V)=0.38, with a WD companion and an accretion disk contributing to the
observed blue excess and moderate Halpha emission. A typical early K-type
main-sequence star with a mass of ~0.75 Msun and a radius of ~0.8 Rsun, would
fill its Roche lobe for a P=0.29585 day orbital period and a more massive WD
companion.
