  A light leptophilic boson (scalar or pseudoscalar) has been postulated to
explain the muon g-2 anomaly and could be a portal to dark matter. Realizing
the leptophilic nature of a singlet boson in the framework of the
two-Higgs-doublet-Model of type-X, we identify the parameter space viable for
the explanation of the updated muon g-2 discrepancy. It is then shown that such
a hypothetical particle will be unambiguously ruled out or discovered via the
Yukawa process at a lepton collider designed as a Higgs factory.
