The signs were subtle. While Prince Harry and girlfriend Chelsy Davy engaged in an amorous lip-lock for all the world to see, the officially unattached William sat dateless beside them in the front row of the royal box at London's Wembley Stadium. Yet every so often during the Concert for Diana—the musical extravaganza William and Harry staged on July 1 in honor of their late mum—William, 25, craned his head round to lock eyes and smiles with a pretty brunette perched two rows back. It was, of course, 25-year-old Kate Middleton—until recently the prince's girlfriend of five years and, in the view of many royal watchers, a princess-in-waiting. That is, until the couple shocked the British public by announcing their split April 14, because, as various theories held:

a. he wasn't ready for marriage
b. she wasn't ready for marriage
c. the constant speculation about a royal engagement proved too much for both.

Now try answer d. Whatever the reason for the split, William is once again courting Middleton—and it appears his charm offensive is meeting with some success. Just last month the prince had his ex to a party at his army barracks in Dorset; the two boogied and reportedly kissed on the dance floor. The night before the Diana concert, Middleton was spotted slipping into William's home in London's Clarence House near midnight. And, while keeping a discreet distance during the concert, they danced and kissed in the wee hours of the morning at the afterparty. "They are clearly seeing each other," says an intimate of the pair. "But whether they are officially dating is another matter."

What is clear: The once-burned Middleton is determined to play it cool this time around until she has a better idea of where this thing is going, friends say. "Kate isn't going to put herself up for everything again unless their relationship is going somewhere," says one. Meaning, um, an eventual engagement? "I think that's the idea," says the friend.

Even then, she need look no further than Princess Diana's experience to move cautiously. "Much as she loves him, [Middleton] doesn't necessarily want to throw herself into the maelstrom of that life unless she is really sure that was what [William] wanted, too," an insider says. On the rise at the fashion chain Jigsaw, Middleton "can have a wonderful career in the fashion world," notes royals expert Judy Wade. "That would all stop with an engagement. He has to prove to her that somehow he will make it okay for her."

For now the prince and his maybe-girlfriend are doing their best to hide in plain sight. Even at the lavish concert afterparty, they waited for the reveling ranks to thin before getting close. Friends are likely to offer the pair some quality private time at their country estates. "You can see they can't be seen in public together until they sort things out," says a pal. Insiders say they'll stay under the radar at least until summer's end. "If they do get back together properly, it will all be down to them," a friend says. "Why should they tell everyone?"

  • Contributors:
  • Simon Perry/London,
  • Courtney Rubin/London,
  • Liz Corcoran/London.