07/03/2006 at 01:00 AM EDT
Relaxing on the sidelines as Prince William
played polo on June 17, Kate Middleton made it clear she had the role of royal girlfriend (and future fiancée?) down to a science. From her sexy but tasteful polka-dot halter dress and strappy red sandals to her casual banter with William's private secretary, the prince's girlfriend of more than three years "seems completely at ease with the Palace machinery," says royal writer Ingrid Seward. The Palace is looking just as comfortable with Kate and her family. Two weeks ago the 24-year-old budding businesswoman brought mum Carole to a princely polo match, and this time around showed up with kid sister Pippa, 22. One observer even noticed that Kate seemed to walk slightly behind the prince—a bow to royal protocol that would be expected were they to marry. Most important, "Prince Charles likes her very much," says one family friend. "She is delightful. And she's playing it right."