Legend has it that Charles II learned of the execution in 1649 of his father Charles I by the English Parliament when his private chaplain walked into the new King's room in Holland and addressed him as 'Your Majesty'.
For Charles, the name was enough, no additional explanation was required. The name made it clear that his father was dead and that he had assumed the crowns of England, Scotland, and Ireland (this disputed of course by Cromwell and co.)
Another (more likely apocryphal) legend claims that Charles, in a last desperate attempt to save his father's life, sent to the parliamentary captors a signed blank sheet of paper, in order to allow them to write in their own terms for the release of Charles I. Seems a shame that modern crypto won't support this use case.