During a recent lunch at a ski resort in the French Alps, an observer witnessed William and Middleton sharing a very chummy lunch with her parents. Says the onlooker: "William was clearly very close to Kate's father, and every time he spoke to him, William replied, 'Yes, Dad.' "
So, when will an engagement happen?
Oddsmakers are wagering 1 to 2 that Prince William will pop the question soon. "We've seen quite a bit of money, suggesting an engagement is imminent," says Nick Weinberg, a spokesman for the betting house Ladbrokes.
And while nobody knows for sure whether a proposal will happen in June, as some online reports have suggested, someone close to William says the engagement is "a given. It's just a question of when."
For more on Prince William and Kate Middleton's marriage plans, including when he'll pop the question and how she won his heart, pick up the newest issue of PEOPLE, on newsstands Friday