  Aims : The hydrogen-deficient supergiants known as R Coronae Borealis (RCB)
stars might be the result of a double-degenerate merger of two white dwarfs
(WDs), or a final helium shell flash in a planetary nebula central star. In
this context, any information on the geometry of their circumstellar
environment and, in particular, the potential detection of elongated
structures, is of great importance. Methods : We obtained near-IR observations
of V854 Cen with the AMBER recombiner located at the Very Large Telescope
Interferometer (VLTI) array with the compact array (B$\leq$35m) in 2013 and the
long array (B$\leq$140m) in 2014. At each time, V854 Cen was at maximum light.
The $H$- and $K$-band continua were investigated by means of spectrally
dependant geometric models. These data were supplemented with mid-IR VISIR/VLT
images. Results : A dusty slightly elongated over density is discovered both in
the $H$- and $K$-band images. With the compact array, the central star is
unresolved ($\Theta\leq2.5$\,mas), but a flattened dusty environment of $8
\times 11$ mas is discovered whose flux increases from about $\sim$20% in the
$H$ band to reach about $\sim$50% at 2.3$\micron$, which indicates hot
(T$\sim$1500\,K) dust in the close vicinity of the star. The major axis is
oriented at a position angle (P.A.) of 126$\pm$29$\deg$. Adding the long-array
configuration dataset provides tighter constraints on the star diameter
($\Theta\leq1.0$ mas), a slight increase of the overdensity to $12 \times 15$
mas and a consistent P.A. of 133$\pm$49$\deg$. The closure phases, sensitive to
asymmetries, are null and compatible with a centro-symmetric, unperturbed
environment excluding point sources at the level of 3% of the total flux in
2013 and 2014. The VISIR images exhibit a flattened aspect ratio at the 15-20%
level at larger distances ($\sim$1$\arcsec$) with a position angle of
92$\pm$19$\deg$, marginally consistent with the interferometric observations.
Conclusions : This is the first time that a moderately elongated structure has
been observed around an RCB star. These observations confirm the numerous
suggestions for a bipolar structure proposed for this star in the literature,
which were mainly based on polarimetric and spectroscopic observations.

Solar and Stellar Astrophysics