Is there a word for "the king who has a regent"?

As the title says: Is there an established word or phrase for a "regent-ee," as distinct from a reigning monarch who does not have* a regent?

From 1811 to 1820, the future King George IV was prince regent and his father King George III was…?

From 1715 to 1723, Philippe d’Orléans was regent and the infant King Louis XV was…?

The Tongzhi Emperor had* regents of one form or another for essentially his whole reign; he was a…?

From a modern perspective we might say king in name only; but I’m interested in contemporary attested terminology, if any.

I could imagine that there might be attested terms for some kinds of regent-ees (maybe along the lines of "king infant," "king invalid") but not a general term; if you have evidence for any such, that’d make a good answer.

* — As a minor bonus question: is it correct to say "King George III had a regent for the latter part of his reign"? Or is there a better verb for the relationship between sovereign and regent? I’d think that anything like "served under" or "was subject to" would be inappropriate, as would "employed" or "retained."