'DWTS' Contestant Sasha Pieterse Reveals Condition That Caused Her 70-Pound Weight Gain

Actress Sasha Pieterse revealed the details of a devastating medical condition during her Tuesday night appearance on Dancing With the Stars.

Pieterse, 21, opened up about how she gained 70 pounds over the course of two years and what adversity she faced because of it.

"I gained 70-ish pounds over two years," Pieterse said. "It was really, really hurtful the way people reacted. People were saying stuff like, 'She's pregnant,' 'You're fat.' They were angry, they were mad that I look like this. [It was] one of the hardest things I've ever been through."

After all this adversity, the Pretty Little Liars star soon found out why this weight gain occurred.

"I had no idea what was going on and I didn't have any way of solving it," she said. "Very recently I was diagnosed with PCOS, Polycystic Ovary Syndrome, a hormone imbalance. Finally, I knew why this was happening to me."

With that knowledge, the actress was able to take control of her weight, and she was since lost 15 pounds.

As for her dancing, she and partner Gleb Savchenko received a 22 for their Latin dance to Hailee Steinfeld's "Most Girls," a song about wanting to feeling comfortable with your own body.

"I love this song because it really resonates with me about what I've been through and what I'm still going through," she said.

Dancing With the Stars airs Mondays at 8 p.m. EST on ABC.