  The eccentric shape of the debris disk observed around Fomalhaut was first
attributed to Fom b, a companion detected near the belt inner-edge, but new
constraints on its orbit revealed that it is belt-crossing, highly eccentric
$(e \sim 0.6-0.9)$, and can hardly account for the shape of the belt. The best
scenario to explain this paradox is that there is another massive body in this
system, Fom c, which drives the debris disk shape. The resulting planetary
system is highly unstable, which hints at a dynamical scenario involving a
recent scattering of Fom b on its current orbit, potentially with the putative
Fom c.
  Our goal is to give insights on the probability for Fom b to have been set on
its highly eccentric orbit by a close-encounter with the putative Fom c. We aim
to study in particular the part played by mean-motion resonances with Fom c,
which could have brought Fom b sufficiently close to Fom c for it to be
scattered on its current orbit, but also delay this scattering event.
  Using N-body simulations, we found that the generation of orbits similar to
that of Fom b, either in term of dimensions or orientation, is a robust process
involving a scattering event and a further secular evolution of inner material
with an eccentric massive body such as the putative Fom c. We found in
particular that mean-motion resonances can delay scattering events, and thus
the production of Fom b-like orbits, on timescales comparable to the age of the
system, thus explaining the witnessing of an unstable configuration.
  We conclude that Fom b probably originated from an inner resonance with Fom
c, which is at least Neptune-Saturn size, and was set on its current orbit by a
scattering event with Fom c. Since Fom b could not have formed from material in
resonance, our scenario also hints at former migration processes in this
planetary system.
