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We have built the historical light curve of the luminous variable GR 290 backto 1901, from old observations of the star found in several archival plates ofM 33. These old recordings together with published and new data show that forat least half a century the star was in a low luminosity state, with B ~18.After 1960, five large variability cycles of visual luminosity were recorded.The amplitude of the oscillations was seen increasing towards the 1992-1994maximum, then decreasing during the last maxima. The recent light curveindicates that the photometric variations have been quite similar in all thebands, and that the B-V color index has been constant within +/-0.1 m despitethe 1.5m change of the visual luminosity. The spectrum of GR 290 at the largemaximum of 1992-94, was equivalent to late-B type, while, during 2002-2014, ithas varied between WN10h-11h near the visual maxima to WN8h-9h at theluminosity minima. We have detected, during this same period, a clearanti-correlation between the visual luminosity, the strength of the HeII 4686 Aemission line, the strength of the 4600-4700 A lines blend and the spectraltype. From a model analysis of the spectra collected during the whole 2002-2014period we find that the Rosseland radius R_{2/3}, changed between the minimumand maximum luminosity phases by a factor of 3, while T_eff varied betweenabout 33,000 K and 23,000 K. The bolometric luminosity of the star was notconstant, but increased by a factor of ~1.5 between minimum and maximumluminosity, in phase with the apparent luminosity variations. In the light ofcurrent evolutionary models of very massive stars, we find that GR 290 hasevolved from a ~60 M_Sun progenitor star and should have an age of about 4million years. We argue that it has left the LBV stage and is moving to aWolf-Rayet stage of late nitrogen spectral type.

GR 290 (Romano's Star): 2. Light history and evolutionary state