The superstar wowed onlookers on the red carpet at the Today X charity concert last week, in a very revealing emerald green gown that showed off her new slim figure.
It's believed Beyonce turned to the keto diet - the hottest new weight-loss phenomenon sweeping Hollywood - to help lose kilos fast, dropping from 77kgs to 62kgs in just eight weeks.
The keto diet is a low-carb, high-fat eating plan, which advocates claim turns your body into a 'fat-burning machine' and has become a fast favourite with celebrities in 2017 - including Gwyneth Paltrow, Kim Kardashian and now Beyonce.
'Keto is the new black,' one Hollywood trainer said. 'Everyone is doing it - and no-one better than Beyonce!
'She looked amazing on the red carpet, there's no denying that keto works - not just to drop kilos fast, but to look and feel your best.'
Adds a source close to Beyonce: 'She started on the keto diet about two months ago. She wanted to give herself time to heal from the birth and relax into life with twin newborns.
'But once she started on keto she found it really easy. She saw results straight away and she's feeling stronger and healthier than ever. No starving, just amazing weight loss.'
Beyonce has made no secret of her struggle to lose weight over the years. The 36-year-old has kept a low profile since giving birth to twins Sir and Rumo Carter in June, but admits to working hard at maintaining her weight.
'I am not naturally the thinnest woman,' she told Elle. 'I have curves. I have struggled with diets and finding something that works for me.'
'I didn't have a lot of time to lose the weight because I scheduled a show three months after I gave birth, which I would never do again!' she told Cinema Blend.
She also revealed: 'I had to lose 60 pounds [27kg]. They had me on that treadmill. I ate lettuce.'
Since then however, Beyonce says she's learnt to love and respect her body - which is why she's chosen keto, widely approved by experts to lose weight after the birth of her new son and daughter.
For the full story and a detailed guide to the keto diet, see this weeks issue of New Idea - out now.