'I'll Help Mariah Lose 20kg!'

Bangin’ Brit tells her new bestie, ‘You better work (out), b*tch!’

She’s got her best body in years, thanks to her hunky personal-trainer beau Sam Asghari – and now Britney Spears wants him to work his magic to whip Mariah Carey into shape!

Yep, with Mimi wallowing in weight woes since her split from fiancé James Packer last October, we’re told Brit has made it her mission to help a sister slim down after they became fast friends at a recent dinner party in LA.

“Brit asked Sam to give Mariah a complete overhaul, just like he did for her,” spills a fellow guest.

“It’s a gruelling workout, but Brit has never felt fitter.

“She set a goal for Mariah to lose 20 kilos, and promised that she’ll look and feel better than ever!”