Context : In late November 2013 a fifth eruption in five years of the M31 recurrent nova M31N 2008-12a was announced .

Aims : In this Letter we address the optical lightcurve and progenitor system of M31N 2008-12a .

Methods : Optical imaging data of the 2013 eruption from the Liverpool Telescope , La Palma , and Danish 1.54m Telescope , La Silla , and archival Hubble Space Telescope near-IR , optical and near-UV data are astrometrically and photometrically analysed .

Results : Photometry of the 2013 eruption , combined with three previous eruptions , enabled construction of a template lightcurve of a very fast nova , t _ { 2 } \left ( V \right ) \simeq 4 days .
The archival data allowed recovery of the progenitor system in optical and near-UV data , indicating a red-giant secondary with bright accretion disk , or alternatively a system with a sub-giant secondary but dominated by a disk .

Conclusions : The eruptions of M31N 2008-12a , and a number of historic X-ray detections , indicate a unique system with a recurrence timescale of \sim 1 year .
This implies the presence of a very high mass white dwarf and a high accretion rate .
The recovered progenitor system is consistent with such an elevated rate of accretion .
We encourage additional observations , especially towards the end of 2014 .