Super Mario Boards

Tough question. I'm leaning on Prince and Princess because Peach is already a princess so…

It depends on the kingdom's rules on marriage to the crown princess. If we're going by real life rules, he'd either be a prince or royal consort, but if we're going by the rules of a world such as Sonic the Hedgehog, then he'd definitely be a king.

mario would still remain a commoner by choice and the marriage would simply be a label upgrade, not a change in status quo. mario would remain living with luigi in their shared home.