The news comes days after Jenner, 23, spoke of Simmons, 22, during an interview with Vogue Australia.
Talking about potentially marrying him on the May feature, she said: “Maybe. Definitely not now, but maybe one day.”
Though the two were together for quite some time, the model only confirmed their relationship this February during an appearance on The Ellen DeGeneres Show.
According to reports, Simmons was caught partying in Atlantic City, NJ, with friends earlier this month. At one point, he allegedly told his pals that he and Jenner had called it quits last week.
Another source told Page Six the two have broken up, months after Radar reported the stars were being torn apart by their busy schedules.