  We present a near-infrared spectrum of the close, detached white dwarf +
brown dwarf binary WD0137-349 (Maxted et al 2006), that directly reveals the
substellar companion through an excess of flux longwards of 1.95 microns. We
best match the data with a white dwarf + L8 composite model. For ages ~1 Gyr,
the spectral type of the cool secondary is in agreement with the mass
determined by Maxted et al. (2006) from radial velocity measurements (0.053 +/-
0.006Msun), and supports an evolutionary scenario in which the brown dwarf
survived a previous phase of common envelope evolution which resulted in the
formation of this close binary. The brown dwarf is the lowest mass companion to
a white dwarf yet found, and the lowest mass object known to have survived a
common envelope phase. At 1300 < T < 1400K WD0137-349B is also the coolest
known companion to a white dwarf. At a separation a = 0.65Rsun the hemisphere
of the brown dwarf facing the 16,500K white dwarf is being heated through
irradiation. We discuss the possible effects of this additional heating, with
particular relevance to those other close binaries with substellar companions,
the hot Jupiters. We propose future observations to investigate the likely
temperature differences between the ``day'' and ``night'' sides of the brown
dwarf.
