This led to interpretation problems - what if a claimant's father was a rightful monarch, but not recognized by everyone?

The Earl, following his father's death, would become the rightful monarch of England under this alternative path of succession.

You are the rightful monarch and heir, blessed by the Winds.

"You're saying that I am no more the rightful monarch than the current king."

Besides, her grandmother usurped the throne-she isn't a rightful monarch.

"Her own actions betray that she is, at least, no rightful monarch," the king said.

He also wrote to the king, reiterating his stance on violence against a rightful monarch.

The duke declares that he may have won the battle, but he restores absolute power to the rightful monarch, Lear.

Anyway, you are these farmers' rightful monarch, are you not?