"Michael proposed to his girlfriend, Luisana, in November, in front of her family in Argentina," rep Liz Rosenberg says. "They're ecstatic. They're adorable, in love and laugh all day long."
Lopilato, 22, a film and TV actress who stars in the hit Argentinian soap opera, Atraccion x 4, accepted his proposal – and loves the diamond engagement ring from Vancouver jeweler Minichiello that Buble, 34, gave her to seal the deal, a friend of Bublé's tells PEOPLE. "He designed the setting himself. He's very proud to be engaged to her."
The "Lost" and "Home" singer met her after one of his concerts in Buenos Aires in November 2008. "They met at a party the record company threw for him after his show in Buenos Aires," says the friend. "The head of the label wanted to introduce Michael to Argentina's most famous actress. When he met her, he said it was love at first sight."
Their Families Have MetTheir families have met "several times and are all very happy about this union," says the friend.
Lopilato, who shot to stardom as a member of the band Erreway and on the soap opera Chiquititas, is working on her next film, Plumiferos. Bublé is gearing up for his "Crazy Love" tour, which begins in March.
The couple has tried to keep their romance "low-key," says the friend. "She travels with him when she can. She was with him when he recently appeared on David Letterman and when he performed on Australian's Idol X-Factor in front of the Sydney Opera House."
Lopilato may also accompany him to New York City on Jan. 30 when he performs as the musical guest on Saturday Night Live. She even appears in the video of his current hit single, "Haven't Met You Yet."
The couple spent New Year's in Hawaii, where they "had a great time," says the friend.
Bublé was engaged to his longtime girlfriend, singer and actress Debbie Timuss, but split up in November 2005. He also dated The Devil Wears Prada actress Emily Blunt for more than two years, but split with her in 2008.
Bublé and Lopilato haven't set a date for the wedding yet, says Rosenberg.