Margot Robbie ''hesitated'' about starring in 'I, Tonya'.

The 27-year-old singer admits she was nervous about signing up for the movie - which follows the life story of figure skater Tonya Harding - because Tonya's life has been ''so well documented''.

She said: ''I definitely had hesitations in that it's an added responsibility to play a real-life person who is still alive - especially one that's so well documented, that people can obviously compare what I'm doing. But it also provided an incredible resource in my research, so it was kind of a double-edged sword in that respect ...

''I didn't realise that everyone knew it to the extent they did, and everyone had already passed judgment on her. I didn't really know what I was getting myself into in that regard.''

And Margot admits it was ''definitely a challenge'' that people had already made their minds up about Tonya but she enjoyed being able to help people explore it more.

She added: ''It was definitely a challenge but kind of an exciting challenge to approach a situation [where] people had already made up their minds, or thought they knew all about [it], and kind of give them a reason to explore it further and explore another side to the story.''

In the movie, Margot plays Tonya when she was 15-years-old and admits it was ''weird'' putting fake braces on for the role.

She told E! News: ''As 15-year-old Tonya, I actually weirdly looking in the mirror of my mum and my 10-year-old nephew - who's a boy - so I was really confused by that. I was like, 'How does this...?' ''I mean, it was very reminiscent of the era, obviously. I felt very young wearing braces again. I had braces at that age; I remember how painfully self-conscious I was at that age about everything. When I was little, my mum cut my hair short in a bowl cut, too. I obviously am a '90s baby, so the fashion has a sense of nostalgia for me. I felt transformed; I didn't feel like myself.''