  Motivated by what is possibly the first sign of new physics seen at the LHC,
the diphoton excess at $750$ GeV in ATLAS and CMS, we present a model that
provides naturally the necessary ingredients to explain the resonance. The
simplest phenomenological explanation for the diphoton excess requires a new
scalar state, $X(750)$, as well as additional vector-like (VL) fermions
introduced in an ad-hoc way in order to enhance its decays into a pair of
photons and/or increase its production cross-section. We show that the
requiered VL quarks and their couplings can emerge naturally from a complete
framework based on the $SU(3)_L \otimes U(1)_\mathcal{X}$ gauge symmetry.
