  We report the serendipitous detection of a giant X-ray flare from the source
2XMM J043527.2-144301 during an XMM-Newton observation of the high latitude
molecular cloud MBM20. The source has not been previously studied at any
wavelength. The X-ray flux increases by a factor of more than 52 from quiescent
state to peak of flare. A 2MASS counterpart has been identified (2MASS
J04352724-1443017), and near-infrared colors reveal a spectral type of M8-M8.5
and a distance of (67\pm 13) pc, placing the source in front of MBM20. Spectral
analysis and source luminosity are also consistent with this conclusion. The
measured distance makes this object the most distant source (by about a factor
of 4) at this spectral type detected in X-rays. The X-ray flare was
characterized by peak X-ray luminosity of ~8.2E28 erg s-1 and integrated X-ray
energy of ~2.3E32 erg. The flare emission has been characterized with a
2-temperature model with temperatures of ~10 and 46 MK (0.82 and 3.97 keV), and
is dominated by the higher temperature component.
