Transcript for Working out with a math teacher-turned model and Instagram star
Reporter: For millions of people around the world 29-year-old pietro boselli needs no introduction. I am a model with an academia background, funny enough. I have a ph.d. In engineering P P. Reporter: Boselli has been capturing the hearts of men and women ever since he became a viral sensation three years ago as the so-called sexiest math teacher in the world. The first few times I didn't realize I was thinking oh, my god, they're taking pictures of the notes, you know, I'm such a good lecturer. Reporter: Pietro has a history of modeling professionally but he put that career on hold to pursue another in math and engineering. Learning's always been what has driven me. Reporter: But after going viral, the only math people wanted to know was -- How many abs do you have? People say six. It's not really. It's only one piece actually. It's all one piece. Yeah, it's all one piece. Reporter: Some of his most popular posts are of his workouts. So we decided to hit the gym. See? Good effort, I think. When I'm sleeping, I skip. Two more. What are you doing? I mean I have two more pancakes for you. Reporter: For "Nightline" I'm kendis Gibson in New York.
This transcript has been automatically generated and may not be 100% accurate.