The LBV nature of Romano's star (GR 290) in M 33

We report the first spectroscopic study of the LBV candidate GR 290 in M 33 (``Romano's star'') taken in February 2003, showing, besides prominent hydrogen and He I emission lines, the 4630-60 Å blend and weak He II 4686 Å emission typical of Of stars. Our broad-band photometry shows that the star was observed during a phase of minimum optical luminosity, with B=17.91+/- 0.03, and a slightly positive colour index, which we tentatively attribute to an anomalous continuum energy distribution. We argue that GR 290 is indeed an LBV star presently in a high temperature phase, that should be followed - also in a short time - by ample spectroscopic and associated photometric variations.