The Princess Diaries: Royal Wedding by Meg Cabot

For Princess Mia, the past five years since college graduation have been a whirlwind of activity: living in New York City, running her new teen community center, being madly in love, and attending royal engagements. And speaking of engagements. Mia's gorgeous longtime boyfriend, Michael, managed to clear both their schedules just long enough for an exotic (and very private) Caribbean island interlude where he popped the question!