Instagram fitness sensation Jen Selter the 'next Jillian Michaels,' agent says Jen Selter, the Instagram fitness star who has amassed nearly 2 million followers with photos of her shapely rear, has signed a lucrative sports management deal and is being dubbed "the next Jillian Michaels." Selter signed with The Legacy Agency, which represents baseball stars Carl Crawford and ­Johan Santana, NFL players Osi Umenyiora and Reggie Bush, and sports broadcasters Troy Aikman and Dan Hicks. "We believe she can be the next Jillian Michaels," said TLA agent Andrew Witlieb, even though Selter, 20, has no formal fitness training, compared to experienced trainer Michaels, 39, who's a judge on NBC's "The Biggest Loser." Jillian didn't get to where she is until her mid-30s. Jen's going to grow as a person, as a fitness expert, in these next years. She's here for the long term," Witlieb added. The ample-curved Long Island native was working at a gym in March 2012 when she started taking photographs of herself working out. Since then, Selter's gathered 2 million Instagram followers, more than half a million Facebook fans and 200,000 Twitter followers, including 2013 Heisman Trophy winner and soon to be NFL pro Johnny Manziel, Amar'e Stoudemire and Shaquille O'Neal. Selter's rise to Internet stardom was profiled in The Post earlier this month. The story caught the attention of Witleib, who signed Selter to his firm a few days ago. "She was someone I never heard of that had 1.3 million Instagram followers, now 2 million, since the Post story," Witlieb told us. This was a combo of health, wellness and fitness meets social media. This girl's really onto something.