(AP) — Returning to swimming after a 20-month retirement, Michael Phelps is easing back into the sport he once dominated by racing one of his best events. The 18-time Olympic gold medalist will swim the 100-meter butterfly at the Arena Grand Prix on Thursday, his first competition since retiring after the 2012 London Games. Phelps hasn't competed since winning a gold medal in the 400 medley relay in London, where he won his record 22nd Olympic medal. "Just being able to get back into that mentality of competition, that's one thing I really loved the most about it when I was really competing in 2012 and throughout my career," he said after practice Wednesday. Phelps resumed training last fall at North Baltimore Aquatic Club in his hometown, spurred on by a younger group of swimmers. Phelps was noncommittal about whether his comeback would lead to swimming in the 2016 Rio Olympics, although he admitted that if he wants to compete at the highest level, he has to be ready by this summer.