  We present the discovery of the shortest-period, non-interacting, white
dwarf-brown dwarf post-common-envelope binary known. The K2 light curve shows
the system, EPIC 21223532 has a period of 68.2 min and is not eclipsing, but
does show a large reflection effect due to the irradiation of the brown dwarf
by the white dwarf primary. Spectra show hydrogen, magnesium and calcium
emission features from the brown dwarf's irradiated hemisphere, and the mass
indicates the spectral type is likely to be L3. Despite having a period
substantially lower than the cataclysmic variable period minimum, this system
is likely a pre-cataclysmic binary, recently emerged from the common-envelope.
These systems are rare, but provide limits on the lowest mass object that can
survive common envelope evolution, and information about the evolution of white
dwarf progenitors, and post-common envelope evolution.
