  We report the serendipitous discovery of a flare star observed with the ROSAT
X-ray observatory. From optical spectra, which show strong and variable
emission lines of the hydrogen Balmer series and neutral helium, we classify
this object as a M3.0Ve star, and estimate a distance of 52 pc from published
photometry. Due to the star's close proximity (13.6') to the calibration source
and RS CVn binary AR Lacertae, long term X-ray coverage is available in the
ROSAT archive (~50 hours spanning 6.5 years). Two large flare events occurred
early in the mission (6-7/1990), and the end of a third flare was detected in
6/1996. One flare, observed with the Position Sensitive Proportional Counter
(PSPC), had a peak luminosity Lx=1.1x10^{30} erg/s, an e-folding rise time of
2.2 hours and a decay time of 7 hours. This decay time is one of the longest
detected on a dMe star, providing evidence for the possibility of additional
heating during the decay phase. A large HRI flare (peak Lx=2.9x10^{30} erg/s)
is also studied. The "background" X-ray emission is also variable - evidence
for low-level flaring or microflaring. We find that >=59% of the HRI counts and
>=68% of the PSPC counts are due to flares. At least 41% of the HRI exposure
time and 47% of the PSPC are affected by detectable flare enhancement.
