Exclusive: Britney Spears Engaged to Jason Trawick!

The pop superstar, 30, is now engaged to her former manager, a source confirms to Us Weekly.  Trawick popped the question on Thursday night, his 40th birthday, when he and the "I Wanna Go" singer shared a romantic private dinner. "Yes, we are engaged," Trawick later told Access Hollywood, adding that both he and his wife-to-be are "over the moon." "This is something they've both wanted for a long time," the source explains to Us. "It's a way to cement their family. They're both extremely happy and can't wait to become man and wife." The spouses-to-be plan to celebrate their engagement Friday night at Planet Hollywood in Las Vegas.

Spears coyly hinted at the big news on Twitter Friday morning, writing: "OMG. Last night Jason surprised me with the one gift I've been waiting for. Can't wait to show you! SO SO SO excited!!!! Xxo" (After wrapping her Femme Fatale world tour in Puerto Rico last weekend, Spears and Trawick -- along with Sean Preston, 6, and Jayden, 5, her sons with ex Kevin Federline -- moved to a 10,000 square-foot estate outside of L.A.) The duo first met in 2006 in a professional capacity. Then at William Morris Endeavor Entertainment, Trawick began representing the "Hold It Against Me" singer while she was still wed to Federline, 33.

(Spears, who dated Justin Timberlake for three years until 2002, also famously wed childhood pal Jason Alexander in 2004 in a Las Vegas marriage that was annulled within 55 hours.) Following her late 2006 split from Federline and tough personal struggles in 2007 and 2008, Trawick proved himself to be a true friend to Spears during some of her darkest hours. Indeed, a source told Us earlier this year, Trawick "was one of the only people who stuck by her through everything."

By 2009, an on-the-mend Spears was ready to take their friendship to the next level. "Britney has liked Jason for a long time," a source explained in April. "The fact that they were great friends gave them a foundation for a solid relationship." The former teen queen "made the first move," she told Us -- and he quickly took a shine to her adorable little boys. "Jason is just amazing with the boys," the multi-platinum singer raved to Us. "They look up to him so much -- they adore him. He's their hero."

"We have such a great time together!" Spears added back in April. (Trawick, who underwent an impressive body makeover and lost 50 pounds in the past two years, even made his acting debut alongside his world-famous girlfriend in her sexy "Criminal" video earlier this year.) "He makes me laugh, and we are so comfortable being ourselves," Spears said of her guy. "I've never been happier."