  We present time-resolved optical spectroscopy of V458 Vulpeculae (Nova Vul
2007 No. 1) spread over a period of 15 months starting 301 days after its
discovery. Our data reveal radial velocity variations in the HeII {\lambda}5412
and HeII {\lambda}4686 emission lines. A period analysis of the radial velocity
curves resulted in a period of 98.09647 \pm 0.00025 min (0.06812255 \pm
0.00000017 d) which we identify with the orbital period of the binary system.
V458 Vul is therefore the planetary nebula central binary star with the
shortest period known. We explore the possibility of the system being composed
of a relatively massive white dwarf (M1 \gsim 1.0 Msun) accreting matter from a
post-asymptotic giant branch star which produced the planetary nebula observed.
In this scenario, the central binary system therefore underwent two
common-envelope episodes. A combination of previous photoionisation modelling
of the nebular spectra, post-asymptotic giant branch evolutionary tracks and
the orbital period favour a mass of M2 \sim 0.6 Msun for the donor star.
Therefore, the total mass of the system may exceed the Chandrasekhar mass,
which makes V458 Vul a Type Ia supernova progenitor candidate.
