Credit: GSI Media (2)

My, how she's grown!

A newly-engaged LeAnn Rimes flaunted a noticeably bustier figure Thursday while sporting a teeny bikini during her vacation in Cabo San Lucas, Mexico with fiance Eddie Cibrian, 37.

"She recently got a boob job," a source reveals to "She’s always, always been insecure about her size. She was a small A-cup. She often talked about wanting to get implants. She’d say, “I just want a little bit so they’re proportionate to my body.'"

To pump up her new appearance, Rimes even turned to the same plastic surgeon Cibrian's ex wife Brandi Glanville used -- and got the same cup size!

Says the insider, "When Brandi and LeAnn were constantly fighting, one of LeAnn's jabs at Brandi was that she was plastic. Brandi replied, 'Be careful, honey. That's what Eddie likes. You'll be there someday too.' Looks like Brandi was right!"

The singer, 28, flaunted her new look while celebrating her engagement to Cibrian. "Cabo!!!!! Sun, bikinis, friends, food, tequila...celebration!!!! Gonna be the best trip!!" Rimes tweeted.

Rimes admitted to Shape last year that she works hard to maintain her picture-perfect bod.

"I'm a competitive person in a lot of ways, so I like a little bit of pressure," she told the mag. "It makes me get to the gym sometimes when I don't want to go, so in that respect it is good, but I try not to let it rule my life."