  Using FORS2 on the Very Large Telescope, we have astrometrically monitored
over a period of two months the two components of the brown dwarf system WISE
J104915.57-531906.1, the closest one to the Sun. Our astrometric measurements -
with a relative precision at the milli-arcsecond scale - allow us to detect the
orbital motion and derive more precisely the parallax of the system, leading to
a distance of 2.020+/-0.019 pc. The relative orbital motion of the two objects
is found to be perturbed, which leads us to suspect the presence of a
substellar companion around one of the two components. We also perform VRIz
photometry of both components and compare with models. We confirm the flux
reversal of the T dwarf.
