Then, sometimes, it was Your Highness. Or Your Majesty -- we know when a king was first called that, a sobriquet formally reserved to emperor, but one king, signing a treaty with the Holy Roman Emperor, insisted on equality of address. And of course Highness for princes or princesses came later. (Henry VII's daughter Mary was Lady Mary until she was the betrothed wife of a Scottish prince.)
But once that was settled, you start to get adjectives. Your Most Serene Highness. His Britannic Majesty. Etc.
So -- I ponder what the royalty will be called. In two separate stories, no less.
One it's fairly easy. Late Middle Ages, you can still flatter a queen by calling her Majesty rather than Grace. Perhaps, with all their extravagant etiquette and elaborate gallantries, a few flights of fancy such "Most high and happy princess."
The other one is steampunk. Which is, to put it mildly, rather more ornate. The adjectives were in full force -- this was, after all, the end of the process. It did not hurt that the climbing middle classes and all made noble and royal position all that much more insecure, so that they were at pains to emphasize distinctions, to shore up the system. Royalty married royalty in those days. Queen Victoria got rather stiff letters from Germanic cousins about how she considered the offspring of morgantic marriages to be fit mates for royalty -- and wrote back, rather sharply, that if she considered them suitable, she did not see how they had any grounds for objection. (And then she let one of her daughters go and marry a subject.)
Which brought me to the seven worlds and pondering what they would deem appropriate. One would prefer elaborate, high-faluting titles -- probably different adjectives for each prince and princess by order of birth (Your Serene Highness, Your Most Gracious Highness, etc.) -- and dovetail them all into a system, somewhat complicated by the question of getting them all to harmonize. Another would like the elaborate but prefer floral and poetic to strictly accurate. A third would take them casually and use the most commonplace title of the current day. Two others would somewhat belligerently tend to use old-fashion address. A sixth would also use the most commonplace title, out of a love of order and not considering fancy address more important than substance. The seventh -- hmm -- that's the odd one. They would probably use the commonplace ones, partly out of a rigid, even repressive sense of order, and partly out of a belief that it did not, in fact, matter very much in the scheme of things.