  For a long time XMMU J010331.7-730144 was proposed as a high-mass X-ray
binary candidate based on its X-ray properties, however, its optical behaviour
was unclear - in particular previous observations did not reveal key Balmer
emission lines. In this paper we report on optical and X-ray variability of the
system. XMMU J010331.7-730144 has been monitored with the Optical Gravitational
Lensing Experiment (OGLE) in the I and V-bands for the past 9 years where it
has shown extremely large amplitude outbursts separated by long periods of
low-level flux. During its most recent optical outburst we obtained spectra
with the Southern Africa Large Telescope (SALT) where, for the first time, the
H-alpha line is seen in emission, confirming the Be nature of the optical
companion. The OGLE colour-magnitude diagrams also exhibit a distinct loop
which is explained by changes in mass-loss from the Be star and mass outflow in
its disc. In the X-rays, XMMU J010331.7-730144 has been monitored by the Neil
Gehrels Swift Observatory through the S-CUBED programme. The X-ray flux
throughout the monitoring campaign shows relatively low values for a typical
Be/X-ray binary system. We show, from the analysis of the optical data, that
the variability is due to the Be disc density and opacity changing rather than
its physical extent as a result of efficient truncation by the NS. The
relatively low X-ray flux can then be explained by the neutron star normally
accreting matter at a low rate due to the small radial extent of the Be disc.
