The 31-year-old singer has reportedly lost an incredible 20kg thanks to the Sirt Food diet. And she has also taken up reformer pilates.

But she has slimmed down so much that people no longer recognise her.

That was the case at an Oscars after-party at the Chateau Marmont in LA.

Polish TV presenter Kinga Rusin had no idea it was Adele when they started chatting at Jay Z and Beyonce’s Oscars party.

Adele, who was wearing a high-neck, long-sleeved, leopard print dress by Aussie designers Ralph and Russo, struck up a conversation with Rusin because the host kept her heels on rather than changing into the slippers guests were presented with when arriving at the party.

“Honestly, I didn’t recognise her because she is so thin now,” Kinga wrote on her Instagram post, which has since been deleted.

While there was a photo ban at the party, Kinga snuck in a selfie with Adele.

After chatting with the British singer, Kinga said she also spoke to Rihanna, competed in a dance off with Jay Z and then danced some more with Leonardo DiCaprio.

It’s not the first time Adele hasn’t been recognised.

On Christmas Eve, the singer shared an Instagram snap of her looking glamorous and while most of the comments were positive, some had her confused with actress Sarah Paulson, who stars in American Horror Story.

“Is it you Adele or woah?” one person asked.

What is the Sirt Food diet?

Adele reportedly followed this diet, which claims to turn on your skinny genes.

The two-phase eating plan switches on sirtuin genes, which help ramp up your metabolism, increase muscle efficiency and reduce inflammation.

“Sirtfoods” are foods such as walnuts, strawberries, coffee and kale which activate the body’s sirtuin genes, essentially mimicing the effects of fasting and exercise.