I think the correct, traditional form of address is to use the highest
title, just as Charles is Charles, the Prince of Wales above all his other
titles, but his sons who are also princes are Prince William and Prince
Harry of Wales.
In all the other royal families the heir to the throne is always called
'Crownprince' but in Britain they never say that. Maybe it's because the
English are famous for lazy speech and like to abbreviate everybody's name.
To my horror I have noticed that they have even begun to call William
'Wills' - all in the guise of endearment, no doubt. The greater reduction of
syllables to one's name equals the greater degree of affection to which one
(Strange that none of them live in Wales.)
Nor did the earlier princes of Wales hundreds of years earlier.
Real good advertisement for Wales isn't it. I mean, all them Princes of
Wales and not one ever wanting to hang around there. Must be one damned
awful place - far from civilisation. Not exactly what a Londoner would call
'home from home'! Why don't a Welsh journalist interview Charles in Welsh,
just for a laugh?