  We report on the discovery of a very low mass (VLM) star in the solar
neighborhood, originally identified as an optical counterpart of a flaring
X-ray source detected in the ROSAT All-Sky survey. Optical spectroscopy and
infrared photometry consistently reveal a spectral type of M9 \pm 0.5 and a
distance of ~11 pm 2pc. The optical counterpart of 1RXS J115928.5-524717 shows
a large proper motion of 1.08\pm0.06 "/year. 1RXS~J115928.5-524717 is the
fourth object among the VLM stars displaying a huge X-ray flare, reaching the
unprecedent value of L_X/L_{bol}~0.1.
