The Voice coach sat in the front row with a group of friends at the 2013 Victoria's Secret Fashion Show to watch Prinsloo walk the runway on Wednesday, Us Weeklyreported.
"[They] stood and cheered for Behati when she walked by," an eyewitness source told Us. "He was a proud fiance. They were the only group going really crazy for any model. Behati would look over and blow him a kiss."
Levine, 34, and Prinsloo, 24, got engaged in July. The couple had reconciled after they split in late spring and Levine briefly dated Sports Illustrated model Nina Agdal. Levine and Prinsloo began dating last year after the Maroon 5 frontman and ex-girlfriend Anne Vyalitsyna, another Victoria Secret model, called it quits.
Ironically, this week's show wasn't the first time Levine had made an appearance at a Victoria's Secret Fashion Show in support of a significant other.
Just two years ago, in 2011, the singer serenaded Vyalitsyna as she walked the runway. He was dating her at the time and performed "Moves Like Jagger" onstage with his Maroon 5 band. The couple held hands during the show and Levine even kissed Vyalitsyna on the cheek. The pair started dating in 2010.
When Levine and Vyalitsyna broke up in April 2012, Levine was reportedly "blindsided."
"Adam's heartbroken," a source told Us at the time. "He wasn't even sure they were really broken up."
Levine reportedly thought they were still together just a month prior to their breakup.