  Three decades of searches have revealed 154 Wolf-Rayet (WR) stars in M31,
with 62 of WC type, 92 of WN type and zero of transition type WN/C or WC/N. In
apparent contrast, about two percent of the WR stars in the Galaxy, the LMC and
M33 simultaneously display strong lines of carbon and nitrogen, i.e. they are
transition type WN/C or WC/N stars. We report here the serendipitous discovery
of M31 WR 84-1, the first transition star in M31, located at RA = 00:43:43.61
DEC = +41:45:27.95 (J2000). We present its spectrum, classify it as WN5/WC6,
and compare it with other known transition stars. The star is unresolved in
Hubble Space Telescope narrowband and broadband images, while its spectrum
displays strong, narrow emission lines of hydrogen, [NII], [SII] and [OIII];
this indicates a nebula surrounding the star. The radial velocity of the
nebular lines is consistent with that of gas at the same position in the disc
of M31. The metallicity at the 11.8 kpc galactocentric distance of M31 84-1 is
approximately solar, consistent with other known transition stars. We suggest
that modest numbers of reddened WR stars remain to be found in M31.
