With the implication, I take it, that the REAL, de iure, Charles III of Great Britain actually died in 1788. Perhaps, given his interest in learning from many sources (about "faiths", for instance), an appropriate, indeed a fitting, title for the current illegitimate usurper might be "Charles the Absorbent". Quite closely, indeed snugly and comfortably, fitting, some might recognise, given his recorded views.