Rita Ora reportedly suffered "hardcore" exercise classes to keep up with Rihanna's svelte shape.
The slim British singer recently checked into a "fat camp" in Austria to blitz any wobbly bits and get herself looking amazing for her upcoming tour.
The extreme boot camp sees patients taking Epsom salts, which act as a diuretic, and eating plain boiled potatoes and boring broths.
"Rita was pushed to the limit by the hardcore exercise regimes in the clinic," an insider confessed to British magazine Star.
The 22-year-old was apparently also advised to chew each mouthful of food 30 times to help her decrease her calorie intake.
Sources also hinted that Rita's sudden interest in weight loss has something to do with her admiration for fellow singer Rihanna.
In the past, Rita has been criticised for copying Rihanna's clothing choices and was even dubbed the Barbadian singer's "understudy" by rapper Azealia Banks.
The girls are both managed by Jay-Z's Roc Nation music label and rumours of a feud emerged when Rita sported strikingly similar outfits to Rihanna's.
However, the UK star remains unfazed by the comparisons and is even flattered by any remarks the two have a similar style.
"I take it as a compliment. She's so cool," Rita previously said.
Rihanna meanwhile has been showing off her amazing figure in a series of photos on Instagram.
Pictures taken in Miami show the toned 25-year-old in a tiny bikini and posing for the camera.
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