Hartley, who is currently partying in LA with Cheryl Cole's ex and her close friend Melissa Niak, appeared in lads' magazine Nuts when she was aged 14.
The 20-year-old student sparked a police investigation after she was pictured flashing in the publication. Nuts were forced to offer an apology after Hartley's teacher at Sheffield School for Girls alerted the authorities about the snap.
According to The Sun, she also "sparked uproar" when she sent a video of herself using a sex toy to her boyfriend's mobile when she was only 15. The clip was then apparently passed around to his friends.
Speaking about the incidents, she said: "I'm ashamed about both and have attempted to learn from my juvenile mistakes."
Hartley and Niak, who have been photographed sunbathing with Cole, have both denied sleeping with the England footballer.
