Margot Robbie became Harley Quinn IRL to study Jared Leto's Joker in 'Suicide Squad'

Actress Margot Robbie has revealed she had to apply tactics of a psychologist to know her Suicide Squad co-star Jared Leto better as he was always in character and it was a task to know his real side.

The 26-year-old star said she found it hard to "get through to him at first," reported Female First.

"He's in character all the time. I spent a lot of time trying to figure out their relationship. Because he's got this facade up, it was really hard for me to get through to him at first. So I was like, okay, I gotta approach this as if I'm trying to crack the Joker," Robbie said.

"It's a test that psychologists use to determine what mental illness people might have. It's a list of 500 questions or something. Whenever we had time to rehearse or improvise, or even in scenes, I'd just start with those questions ... I'd see which ones would catch him off guard and how, how he'd react, and I'd be like, 'Okay, I'm gonna go for this tactic now.'"