  We propose a common envelope evolution (CEE) scenario where a red giant
branch (RGB) star engulfs a planet during its core helium flash to explain the
puzzling system WD 1856+534 where a planet orbits a white dwarf (WD) of mass
0.52Mo with an orbital period of 1.4 day. At the heart of the scenario is the
recently proposed assumption that the vigorous convection that core helium
flash of RGB stars drive in the core excite waves that propagate and deposit
their energy in the envelope. Using the binary-MESA stellar evolution code we
show that this energy deposition substantially reduces the binding energy of
the envelope and causes its expansion. We propose that in some cases RGB stars
might engulf massive planets of ~0.01Mo during their core helium flash phase,
and that the planet can unbind most of the mass of the bloated envelope. We
show that there is a large range of initial orbital radii for which this
scenario might take place under our assumptions. This scenario is relevant to
other systems of close sub-stellar objects orbiting white dwarfs, like the
brown dwarf-WD system ZTFJ003855.0+203025.5.
