  We report the discovery of a bright transient X-ray source, CXOU
J132518.2-430304, towards Centaurus A (Cen A) using six new Chandra X-Ray
Observatory observations in 2007 March--May. Between 2003 and 2007, its flux
has increased by a factor of >770. The source is likely a low-mass X-ray binary
in Cen A with unabsorbed 0.3-10 keV band luminosities of (2-3) x 10^{39} erg
s^-1 and a transition from the steep-power law state to the thermal state
during our observations. CXOU J132518.2-430304 is the most luminous X-ray
source in an early-type galaxy with extensive timing information that reveals
transience and a spectral state transition. Combined with its luminosity, these
properties make this source one of the strongest candidates to date for
containing a stellar-mass black hole in an early-type galaxy. Unless this
outburst lasts many years, the rate of luminous transients in Cen A is
anomalously high compared to other early-type galaxies.
