"Yes, we are engaged," Trawick told "Access Hollywood" on Friday, kvelling that he's "over the moon, as [is] she."
Britney dropped a Twitter hint about the nuptial news on Friday morning, enthusing, "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."
Jason got down on bended knee on Thursday evening, which also happened to be his 40th birthday.
"He surprised her after she gave him his gifts and after they had cake," an insider tells People.
Brit's sons, Sean, 6, and Jayden, 5, witnessed the event.
"This is something they've both wanted for a long time," a source tells Us Weekly. "It's a way to cement their family. They're both extremely happy and can't wait to become man and wife."
TMZ says the low-key couple of two-plus years will have a joint birthday and betrothal celebration on Friday night in Las Vegas, the scene of her ill-fated, 55-hour 2004 marriage to childhood friend Jason Alexander.
The shindig will play to Brit-Brit's sweet tooth by kicking off at the Chocolate Lounge at the Sugar Factory in the Paris Hotel, where guests will partake of chocolate fondue and chocolate truffle cigars. Later, the festivities will move to the nearby Chateau nightclub.
According to TMZ, Trawick asked Spears' dad, Jamie, for her hand, which is both an old-fashioned courtesy and a legal necessity: She's still under that post-meltdown conservatorship overseen by her father.
As for the ring, size apparently matters. Keep clicking for details ...