  We present the discovery of a 3h5m orbital-period binary star at the heart of
the planetary nebula M 3-1 - the shortest period photometrically-variable
central star known and second only to V458 Vul, in general. Combined modelling
of light and radial velocity curves reveals both components to be close to
Roche-lobe-filling, strongly indicating that the central star will rapidly
evolve to become a cataclysmic variable, perhaps experiencing a similar
evolution to V458 Vul resulting in a nova eruption before the planetary nebula
has fully dissipated. While the short orbital period and near Roche-lobe
filling natures of both components make the central binary of M 3-1 an
important test case with which to constrain the formation processes of
cataclysmic variables, novae and perhaps even supernovae type Ia.
