  We present the discovery of an L0 companion to the nearby M1.5 dwarf G
239-25, at a projected distance of 31 AU. It is the faintest companion
discovered so far in our adaptive optics survey of all known M dwarfs within 12
pc, and it lies at the stellar/substellar limit. Given the assumed age of the
primary star, the companion is likely an extremely low mass star. The long
orbital period of G 239-25 AB ($\approx 100$ years) precludes a direct mass
determination, but the relatively wide angular separation will allow detailed
analyses of its near infrared and visible spectra.
