  Hot subdwarf B stars (sdBs) are evolved core helium-burning stars with very
thin hydrogen envelopes. In order to form an sdB, the progenitor has to lose
almost all of its hydrogen envelope right at the tip of the red giant branch.
In binary systems, mass transfer to the companion provides the extraordinary
mass loss required for their formation. However, apparently single sdBs exist
as well and their formation is unclear since decades. The merger of helium
white dwarfs leading to an ignition of core helium-burning or the merger of a
helium core and a low mass star during the common envelope phase have been
proposed. Here we report the discovery of EC 22081-1916 as a fast rotating,
single sdB star of low gravity. Its atmospheric parameters indicate, that the
hydrogen envelope must be unusually thick, which is at variance with the He-WD
merger scenario, but consistent with a common envelope merger of a low-mass,
possibly substellar object with a red-giant core.
