  Planets can form and survive in close binaries, although dynamical
interactions with the secondary component can actually significantly impact the
giant planet formation and evolution. Rare close binaries hosting giant planets
offer therefore an ideal laboratory to explore the properties and the stability
of such extreme planetary systems. In the course of our CFHT and VLT
coronographic imaging survey dedicated to the search for faint companions of
exoplanet host stars, a close (about 20 AU) secondary stellar companion to the
exoplanet host HD196885 A was discovered. For more than 4 years, we have used
the NaCo near-infrared adaptive optics instrument to monitor the astrometric
position of HD196885 B relative to A. The system was observed at five different
epochs from August 2005 to August 2009 and accurate relative positions were
determined. Our observations fully reject the stationary background hypothesis
for HD196885 B. The two components are found to be comoving. The orbital motion
of HD196885 B is well resolved and the orbital curvature is even detected. From
our imaging data combined with published radial velocity measurements, we
refine the complete orbital parameters of the stellar component. We derive for
the first time its orbital inclination and its accurate mass. We find also
solutions for the inner giant planet HD196885 Ab compatible with previous
independent radial velocity studies. Finally, we investigate the stability of
the inner giant planet HD196885 Ab due to the binary companion proximity. Our
dynamical simulations show that the system is currently and surprisingly more
stable in a high mutual inclination configuration that falls in the Kozai
resonance regime. If confirmed, this system would constitute one of the most
compact non-coplanar systems known so far. It would raise several questions
about its formation and stability
