"Marloes and Alex are very much a couple," a spokesperson from Horst's agency, Next Model Management, tells Us. "They met through friends and have been together seriously for a few weeks. It's early days, but they are really happy."
The Endless Love actor has been linked to Dianna Agron and Emma Roberts in the past, and was engaged to Elvis Presley's granddaughter Riley Keough. To celebrate his birthday, he and his new lady love visited Disneyland in Anaheim, Calif., with a group of friends.
"Happy birthday baby @a1pettyfer #birthdayboy," Horst, 25, captioned a photo with her new beau on April 10.
Horst has modeled for Victoria's Secret, H&M, and DKNY. Earlier this week, she was named the new face of Maybelline.
(E! News was first to report the coupling.)