  A sterile neutrino with a keV-scale mass is a compelling dark matter
candidate. We propose a new production mechanism involving the decay and
annihilation of a complex scalar singlet with a Higgs portal coupling which
develops a vacuum expectation value. The interactions of the resulting pseudo
Nambu-Goldstone boson may thermalise the dark sector. We determine the region
of parameter space where dark sector thermalisation is reached and discuss the
most relevant cosmological observables. The scenario can be considered as the
combination of a freeze-in of the dark sector followed by relativistic
freeze-out.
