By Alex Tresniowski
May 03, 2010 12:00 PM

High in the French Alps, in the ski resort region of Courchevel on a gorgeous spring day, Prince William lunched with his girlfriend Kate and an older gent he called “Dad.” A lovely scene all around, except the man isn’t Will’s pop, Prince Charles-he is Kate’s father, Michael Middleton, who (with wife Carole and children Pippa and James) joined the couple at Le Bel Air restaurant during a ski holiday this March. “William was clearly very close to Kate’s father, and every time he spoke to him, William replied, ‘Yes, Dad,'” said an onlooker who watched them share a cozy meal. “Everyone in their group was laughing, and it was clearly jokey, but William did look part of the family.”

He isn’t, officially-nor is Kate calling Charles “Dad” just yet-but from the looks of things it might not be too long now. The question of if and when the pair will marry is back in the headlines after one report suggested a June engagement announcement and a wedding some time in 2010 (see box). One Palace insider tells PEOPLE that report is “wrong on every possible count,” while several sources in the couple’s circle insist Will and Kate will get engaged when they’re good and ready. Still, says someone close to Will, that the prince will propose to his patient princess-to-be is “a given. It’s just a question of when.”

After all, it was Will himself who once told a reporter, “I’m only 22, for God’s sake. . . . I don’t want to get married until I’m at least 28.” This June 21 he turns 28. For Kate, the long courtship has been a blessing and a curse. She has, say friends, had time to get used to the life she would lead as part of the Windsor family. But she’s also been mocked by British tabs-dubbed “Waity Katie,” content to club-hop until she gets her ring. Kate is aware of the jabs, says a friend of the couple’s, and “she says, ‘I won’t let it bother me.'” Says a Kate pal: “It’s an insult to assume she’s some pathetic waif waiting for her big day. She’s an intelligent woman who has discussed this with her boyfriend, and they’ll make their minds up in their own time.”

If anything, say those who know her, their lengthy romance proves Kate, 28, knows how to keep her prince happy-and handle the scrutiny that will come with being his wife. Since meeting him at the University of St. Andrews in 2001, the lithe, stylish Kate has won William’s heart with her love of sports, sense of fun and ability to hold her own opposite a boyfriend who happens to be second in line to the throne. Together they weathered a brief 2007 breakup (they reconnected a few months later), after which Kate kept a deliberately low profile (working for a fashion retailer and, more recently, her family’s party-supply business)-all while accompanying Will on vacations with Prince Charles and earning royal approval with her letter-perfect behavior. “She has shown she is discreet and dignified, and she will make a fantastic princess,” says the couple’s friend.

But even more important, says this friend, “it’s about making William happy, and Kate does that.” For one thing, she seems fine with working around Will’s busy schedule and enduring his long absences. Since enrolling in the military in 2006-he’s now training with the Royal Air Force’s helicopter search-and-rescue squad; once he’s done in September, he’ll become a squadron pilot stationed in Anglesey, Wales-the prince has learned to squeeze in his squeeze. He sees her on weekends at his private home near his base in North Wales and on the slopes during short breaks from duty. When they can, they also like to meet up in country pubs and hang out with pals. “Many people they know have boyfriends in the army and go months without seeing each other,” the couple’s friend says. “It’s healthy if you’re not in each other’s pockets.”

The true test for Kate, however, will come after she and Will tie the knot (most agree their wedding would likely happen before 2012, the 60th anniversary of the Queen’s accession). “The minute you get HRH before your name, your life changes beyond recognition,” says Ken Wharfe, a bodyguard for William’s late mother, Princess Diana. But experts believe Kate will have an advantage over Diana if she and Will stay as happy as they seem. “If she and the prince are strong in their marriage,” says Patrick Jephson, Diana’s former private secretary, “then all these other things stand a good chance of coming out good.”

Now if only Britain would get off the couple’s backs about the whole wedding thing. On April 17 the pair attended the nuptials of two friends-something they’ve been doing a lot lately-at the Church of St. Peter in Tiverton, Devon. The bride and groom got all the gifts, but it was Will (in traditional tailcoat and red tie) and Kate (in a stunning scarlet dress) who were “the center of attention,” says one onlooker. Hey, nothing wrong with a little trial run.