  VVV J12564163$-$6202039 is an L subdwarf located in the Galactic plane ($b$ =
0.831 deg) discovered by its high proper motion (1.1 arcsec yr/s). We obtained
an optical to near-infrared spectrum of it with the X-shooter on the Very Large
Telescope, and re-classified it as an sdL3 subdwarf. Its best-fitting BT-Dusty
model spectrum has $T_{\rm eff}$ = 2220 K, [Fe/H] = $-0.9$, and log $g$ = 5.5.
It is just below the stellar/substellar boundary in the $T_{\rm eff}$ versus
[Fe/H] parameter space. This object is at a distance of 66.94$^{+8.49}_{-6.77}$
pc according to the $Gaia$ astrometry. It has a halo membership probability of
99.82 per cent according to its Galactic kinematics. It has unusually flat
(|$Z$| < 500 pc) and extremely eccentric (e = 0.9) prograde orbit that takes
the source from as close as 1.2 kpc from the Galactic centre to 24 kpc out. VVV
J12564163$-$6202039 joined by SDSS J133348.24+273508.8 and ULAS
J021258.08+064115.9 are the only three known objects in the sdL subclass that
have halo kinematics.
