Answer: Princess
"I come as the king's servant, and with his authority".
William arrives at the English camp and is stunned to see a woman, who resembles Murran in many ways, there. It is the Princess of Wales, Isabella, who thinks she has been sent to negotiate a truce with Wallace; in reality, unbeknownst to the Princess, her appearance has been used to buy the English a bit of time to gain conscripts and move them into place.
While the relationship between William and Isabella may have produced an interesting story, the fact of the matter is that at the time of Wallace's execution (1305), Isabella was nine years old and living in France. She did not marry Edward II until 1307; by then, Edward I was dead too. By the way, although there has been much talk about Edward's relationship with Piers Gaveston, he and Isabella did have four children together.