  We propose that the diphoton excess at 750 GeV reported by ATLAS and CMS is
due to the decay of an ${\it exo-Higgs}$ scalar $\eta$ associated with the
breaking of a new $SU(2)_e$ symmetry, dubbed ${\it exo-spin}$. New fermions,
${\it exo-quarks}$ and ${\it exo-leptons}$, get TeV-scale masses through Yukawa
couplings with $\eta$ and generate its couplings to gluons and photons at
1-loop. The matter content of our model yields a $B-L$ anomaly under $SU(2)_e$,
whose breaking we assume entails a first order phase transition. A non-trivial
$B-L$ asymmetry may therefore be generated in the early universe, potentially
providing a baryogenesis mechanism through the Standard Model (SM) sphaleron
processes. The spontaneous breaking of $SU(2)_e$ can in principle directly lead
to electroweak symmetry breaking, thereby accounting for the proximity of the
mass scales of the SM Higgs and the exo-Higgs. Our model can be distinguished
from those comprising a singlet scalar and vector fermions by the discovery of
TeV scale exo-vector bosons, corresponding to the broken $SU(2)_e$ generators,
at the LHC.
