IS IT TREASON TO CHEAT on your husband if he is the heir to the throne?

Sorry, this is somewhat like my other question. Only FOR EXAMPLE; What if Kate had a little fling after the marriage has taken place,(not that she ever will!) She would be endangering the hereditary succession if she gave herself to someone who isn't her husband. What I want to know is this: If a woman marries an heir to the throne and messes around on him, would she be guilty of treason or simply adultery? Thanks for your time,