The 23-year-old singer – who previously dated Paige Turley – was seen locking lips with the “sexually fluid” musician, as he partied alongside the likes of Nicole Scherzinger, Lottie Moss and Ashlee Simpson ahead of the big awards bash.
An eyewitness told The Sun on Sunday newspaper: “Lewis and Yungblud were getting on like a house on fire, toasting each other and having a laugh.
“Then they started snogging in the middle of the party. It was all very light-hearted but they really put on a show.
“Neither of them is afraid of being the centre of attention, so they thought it was hilarious.”
Lewis previously dated Paige on and off from 2014 until 2016.
But the chart-topping star has recently admitted to being unsuccessful in his quest to find love, revealing he’d even signed up to dating apps in a bid to find a new girlfriend.
Speaking about his search for love in 2019, he shared: “There’s no sex, drugs or rock ‘n’ roll for me – you can take out the sex, the drugs, and it’s much more pop music than rock ‘n’ roll.
“The furthest I get is kissing and a beer.”
Meanwhile, Yungblud previously dated Halsey for almost a year before they split up in September.
The 22-year-old musician also opened up about his own sexual fluidity in 2019.
He explained: “It’s about connection, I’m very fluid about it.
“I came to London to be liberated, to be able to paint my nails, try sex with a guy, every-thing, to fulfil fantasies and figure out who I am.”