I have been sorting some old coins left to me by my father and have come across what seems to be a 1790 George IV Guines coin but the legend is not the same as in the Catalogue. My coin has a "G.L.REX.F.D.M.C.M.D.S.T.M.S.P.E.T.C." legend on it. I would appreciate if anyone can help me identify this coin.

Thanking you in advance if you can assist.