  CXOM31 J004252.030+413107.87 is one of the brightest X-ray sources within the
D_25 region of M31, and associated with a globular cluster (GC) known as B135;
we therefore call this X-ray source XB135. XB135 is a low mass X-ray binary
(LMXB) that apparently exhibited hard state characteristics at 0.3--10 keV
luminosities 4--6 E+38 erg/s, and the hard state is only observed below ~10%
Eddington. If true, the accretor would be a high mass black hole (BH) (> ~50
M_Sun); such a BH may be formed from direct collapse of a metal-poor, high mass
star, and the very low metalicity of B135 (0.015 Z_Sun) makes such a scenario
plausible. We have obtained new XMM-Newton and Chandra HRC observations to shed
light on the nature of this object. We find from the HRC observation that XB135
is a single point source located close to the center of B135. The new
XMM-Newton spectrum is consistent with a rapidly spinning ~10--20 M_Sun BH in
the steep power law or thermal dominant state, but inconsistent with the hard
state that we previously assumed. We cannot formally reject three component
emission models that have been associated with high luminosity neutron star
LMXBs (known as Z-sources); however, we prefer a BH accretor. We note that
deeper observation of XB135 could discriminate against a neutron star accretor.
