  One of the main features of a Two-Higgs Doublet Model (2HDM) is the presence
of two additional neutral Higgs states, besides the one mimicking the ~125 GeV
state observed at the LHC. The three Higgs bosons of a 2HDM can be produced at
the LHC either singly via gluon fusion or in pairs with each other. When
analyzing their pair production, the emphasis is laid on gluon-initiated
processes, and the electroweak (EW) production is generally not treated on the
same footing, assuming its contribution to be highly subleading. We show here
that when the sum of the masses of the lightest scalar and pseudoscalar Higgs
bosons in the Type-I 2HDM is smaller than the Z-boson mass, their EW pair
production can dominate over QCD pair production by orders of magnitude.
