What would happen if a princess fell in love with a servant in medieval times?

I would suspect that such a thing would usually have been hushed up, and so we would have no record of it. But we know that on one occasion, a widowed queen fell in love with her steward. This happened when Queen Catherine of Valois secretly married her steward, Owen Tudor, who was a Welsh commoner. The two subsequently had a number of children. The law of the time dictated that a widowed queen could not marry without permission of the king, and if the king was under age, as her son was, she needed permission of parliament; so the marriage was technically illegal. Nevertheless, no one did anything about it. As fate would have it, a grandson of Queen Catherine and Owen Tudor became king Henry VII and founded the Tudor dynasty.

There is a link below to an article on Catherine of Valois.