  Radial substructure in the form of rings and gaps has been shown to be
ubiquitous among protoplanetary discs. This could be the case in exoKuiper
belts as well, and evidence for this is emerging. In this paper we present ALMA
observations of the debris/planetesimal disc surrounding HD 206893, a system
that also hosts two massive companions at 2 and 11 au. Our observations reveal
a disc extending from 30 to 180 au, split by a 27 au wide gap centred at 74 au,
and no dust surrounding the reddened brown dwarf (BD) at 11 au. The gap width
suggests the presence of a 0.9 M$_\mathrm{Jup}$ planet at 74 au, which would be
the third companion in this system. Using previous astrometry of the BD,
combined with our derived disc orientation as a prior, we were able to better
constrain its orbit finding it is likely eccentric ($0.14^{+0.05}_{-0.04}$).
For the innermost companion, we used RV, proper motion anomaly and stability
considerations to show its mass and semi-major axis are likely in the range
4-100 M$_\mathrm{Jup}$ and 1.4-4.5 au. These three companions will interact on
secular timescales and perturb the orbits of planetesimals, stirring the disc
and potentially truncating it to its current extent via secular resonances.
Finally, the presence of a gap in this system adds to the growing evidence that
gaps could be common in wide exoKuiper belts. Out of 6 wide debris discs
observed with ALMA with enough resolution, 4-5 show radial substructure in the
form of gaps.
