  An excess of low-energy electronic recoil events over known backgrounds was
recently observed in the XENON1T detector, where $285$ events are observed
compared to an expected $232 \pm 15$ events from the background-only fit to the
data in the energy range 1-7 keV. This could be due to the beta decay of an
unexpected tritium component, or possibly to new physics. One plausible new
physics explanation for the excess is absorption of hidden photon dark matter
relics with mass around $2.8$ keV and kinetic mixing of about $10^{-15}$, which
can also explain cooling excesses in horizontal-branch (HB) stars. Such small
gauge boson masses and couplings can naturally arise from type-IIB low scale
string theory. We provide a fit of the XENON1T excess in terms of a minimal low
scale type-IIB string theory parameter space and present some benchmark points
which provide a good fit to the data. It is also demonstrated how the required
transformation properties of the massless spectrum are obtained in intersecting
D-brane models.
