We report the likely optical ID of the bright transient recently discovered in M31, CXOM31 J004253.1+411422 (Henze et al, ATEL #2356). With a peak X-ray luminosity of nearly 5e39 erg/sec, this is the brightest X-ray transient yet found in M31. An approximately 4000 second HST exposure on 21 Jan 2010, using the ACS and F435W filter, finds an apparently new object with m(f435w)=23.8. This object is not seen in an earlier serendipitous 4000 second ACS exposure on 13 October 2004 using the F660N filter.