verb/ɛ.tʁə ply ʁwa.ja.lis.t(ə) kə lə ʁwa/
to be more Catholic than the Pope; to make more effort to defend someone's interests than they make themselves
Literally, “to be more royalist than the king”. From François-René de Chateaubriand, De la Monarchie selon la Charte, Paris, 1816, LXXXI.