Harry Styles and Nadine Leopold
Harry Styles is completely smitten by Victoria's Secret model Nadine LeopoldGetty

One Direction star Harry Styles is reportedly planning to spend his 21st birthday with rumoured girlfriend, Victoria's Secret model Nadine Leopold.

The pair first met back in November through the Austrian model's CAA agent Jeff Azoff, and were pictured on a series of dates before Christmas sparking rumours that they are more than just close friends.

So much so that Styles and Leopold celebrated her 21st birthday together in Los Angeles earlier this month.

"Everyone's teasing him, saying he's in love, and he's not denying it. It's the real deal. He's never felt this way about anyone before," a source told the Sun.

"Harry has spent virtually all his free time in Los Angeles with Nadine. They're infatuated with each other and can't stand being apart. There's nobody else he'd rather be with on his birthday," the insider added.

Styles, who has a history of dating high-profile celebrities including Taylor Swift and Kendall Jenner, was spotted with Leopold at the Go Greek frozen yogurt bar in Beverly Hills on 22 January.

"Harry and Nadine came in together and tried a couple of samples before making their order. Harry had a medium sized frozen yogurt with strawberries and bananas and his friend had the same, but with pineapple and toasted coconut on top. He gave her a bite of his with his spoon and she did the same to him. They seemed cute together. Flirty, like a couple," an eyewitness told Hollywood Life.