Harry Styles is gearing up for his 21st birthday and according to sources, he's planning to make the landmark occasion quite the romantic affair and spending it with his special girl!

The One Direction member will have his Victoria's Secret model girlfriend Nadine Leopold, 21, by his side when he celebrates his big day on Sunday, The Sun reported.

"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," an insider told the outlet.

"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 source added.

The Austrian beauty, who was introduced to Styles by her agent in November, has been keeping herself busy with work commitments, this week jetting off to Istanbul.

And while the pop star is preparing for his band's world's tour, which kicks off in Sydney on Feb. 7, his belle appears to be excitedly looking forward to Valentine's Day.

Recently taking to Instagram to share a shot of herself in sexy black lingerie, she wrote: "Only a few weeks left until Valentine's Day."

It's only a matter of weeks since Leopold herself celebrated her 21st birthday on Jan. 7, and she marked the occasion with Styles by her side.

The two were spotted having dinner at Craig's in West Hollywood, Calif., on Jan. 6, and the following day were spotted celebrating Rande Gerber's Malibu eatery Cafe Habana.

At the time, a source told Us Weekly of the couple's romantic status: "Harry has been getting more serious with Nadine."

The source noted that the two were "spending lots of time together," but were not yet exclusive.