cthia wrote:Underage assumption of the crown isn't at all unprecedented in literature either. I suddenly fear arranged marriages.
At any rate, what came first for Elizabeth? The chicken (husband) or the egg (crown.)
Oh, good point. It seems the egg (crown) came first.
Queen's Gambit in World of Honor has the story of King Roger III's assassination (and aftermath). During that story Elizabeth is already referred to as Queen (so I assume she's formally taken up the crown), but Justin is still "only" a her fiance
"Elizabeth III, Queen of Manticore, stood with her fiancé, Justin Zyrr, in the small ante-chamber into which they had retreated after viewing the holo-video of Roger III's death."
OTOH she was only 16 at the time.
World of Honor: Queen's Gambit wrote:Elizabeth rubbed her hands over her eyes. "By Manticoran law, I must have a regent until I'm twenty-one T-years. Since I'm past my sixteenth birthday, they can't foist just anyone on me. I nominate my regent; Parliament confirms or rejects my choice. We do this until we're both happy. I suspect it could be an ugly time."
She sat in thoughtful silence for a moment, then, twisting in his lap to face him, she twinkled.
"Then there will be the question of our marriage."
Justin felt a sudden, cold fear that somehow Elizabeth would be taken from him. They had been engaged with King Roger and Queen Angelique's full approval since soon after Elizabeth's seventeenth birthday. Could Parliament force Elizabeth to break the engagement, choose another spouse?
"Question?" he squeaked.
This time Ariel's reproving bleek was for both of them—Justin for doubting Elizabeth, and Elizabeth for her choice of a joke. The treecat rose and patted Justin on the side of his face, his other true-hand resting on Elizabeth's shoulder.
"I shouldn't tease," Elizabeth admitted ruefully. "Justin, no one can make me break my engagement with you. I don't even expect it to be questioned. However, the line of succession has just grown shorter by one. Originally, we planned to marry after I turned twenty-one, right?"
"Right," he answered, his voice back to normal.
"Now I expect there will be some pressure for us to marry sooner."
"I don't have a problem with that."
"Nor I, particularly," she said, "but there will be those who do. Some will think a proper mourning period should be observed. Others will worry that the distractions of a wedding, a husband, pressure to produce an heir, will distract me from my duties as Queen."
"So they'll want you to wait."
"Exactly. After all, there are the cadet branches of the House. My Aunt Caitrin and her children can carry on if something happens both to me and to Michael before I have children of my own. . . ."
Her voice trailed off. Small and forlorn, she leaned her head back against his shoulder, tears trailing down her face.
"Justin, I don't want to think about it!"
"Then don't," Justin suggested, "for right now. Don't think about anything at all."
So she was Queen, but needed a regent, and wasn't yet married. The timing of the marriage was going to be subject to political pressures, but apparently not constitutional questions.
So there we are, that seems to be the most relevant text-ev. (And one I didn't think about until your question)