There's no doubting Britney Spears is in great shape after dancing herself svelte during her Circus tour – but what's happened to her breasts?

As the singer strode through the Mexican resort of Zihuatanejo at the weekend, her cleavage looked like it had gone the same way as her more unwanted curves.

Britney is on a sunshine break with agent/boyfriend Jason Trawick, dad Jamie and her two young sons with ex-husband Kevin Federline, Sean Preston and Jayden James.

Despite reports Britney and Jason ended their unconfirmed relationship last month, the pair seemed very much a couple as they relaxed in the sun together, while grandpa Jamie kept the kids amused on the beach.

Take an advance peek at Brit's new video for '3' here.

Roll up! Roll up! It's Britney's Circus...