  We report the discovery, in an Extreme Ultraviolet Explorer (EUVE) short
wavelength spectrum, of an unresolved hot white dwarf companion to the
5th-magnitude B5Vp star HR2875. This is the first time that a non-interacting
white dwarf$+$ B star binary has been discovered; previously, the the earliest
type star known with a white dwarf companion was Sirius (A1V). Since the white
dwarf must have evolved from a main sequence progenitor with a mass greater
than that of a B5V star ($\geq$6.0M$_\odot$), this places a lower limit on the
maximum mass for white dwarf progenitors, with important implications for our
knowledge of the initial-final mass relation. Assuming a pure-hydrogen
atmospheric composition, we constrain the temperature of the white dwarf to be
between 39,000K and 49,000K. We also argue that this degenerate star is likely
to have mass significantly greater than the mean mass for white dwarf stars
($\approx$0.55M$_\odot$). Finally, we suggest that other bright B stars (e.g.\
$\theta$ Hya) detected in the extreme ultraviolet surveys of the ROSAT Wide
Field Camera and EUVE may also be hiding hot white dwarf companions.
