The 20-year-old model revealed as much during a Periscope Q&A this week, relating an adorable story of being too bashful to attend a baseball game with the 26-year-old singer when they were teenagers.
"We actually have been friends since I was like, 13," she shared. "We met at the Grammys, and he asked me to a baseball game and I said no. It was literally because I was like, so nervous I didn't even know what it meant to hang out with a boy."
"I didn't have my phone with me, and I don't think he did either because we were at the Grammys, and so he wrote his number on a piece of paper and gave it to my mom," she recalled. "And then we've been friends ever since. Now we're more than friends."
Hadid and Jonas have been linked since June, and made their first appearance as a couple at the U.S. Open tennis championships Sept. 8. When asked by E! News to describe the model in one word, Jonas replied, "Happiness," in an interview this week.
Hadid is the eldest daughter of Mohamed Hadid and Yolanda Foster, and known for her work with Guess, Maybelline and Seafolly. Jonas came to fame with the Jonas Brothers, and released new single "Cake by the Ocean" with his band DNCE on Sept. 14.