  We present a model-atmosphere analysis of ultraviolet echelle spectra of
KPD0005+5106 taken with the Space Telescope Imaging Spectrograph aboard the
Hubble Space Telescope. The star is the hottest known pre-white dwarf (Teff =
200,000+-20,000 K, log g = 6.7+-0.3; Wassermann et al. 2010). Its atmosphere is
composed of helium with trace amounts of metals. It is of the so-called O(He)
spectral type that comprises very hot helium-rich pre-white dwarfs whose origin
is debated. From neon and silicon ionisation balances, we derive tighter
constraints on the effective temperature (195,000+-15,000 K) and improve
previous abundance determinations of these elements. We confirm the idea that
KPD0005+5106 is the descendant of an R Coronae Borealis (RCB) star and, hence,
is the outcome of a binary-white dwarf merger. We discuss the relation of
KPD0005+5106 to other O(He) and RCB stars.
