'It completely changed the person I am': Jessica Chastain talks about her sister's tragic suicide as she graces magazine cover

Her sister Juliet took her own life after a long battle with depression in 2003.

And Jessica Chastain has spoken about the tough subject in the accompanying interview for her upcoming Instyle cover.

In the January issue of the publication, the 37-year-old actress revealed that she was devastated by her younger sister's death over a decade ago but believes the experience has helped her stay grounded.

Scroll down for video 

Pretty in purple: Jessica Chastain is on the cover of the January issue of InStyle magazine

Pretty in purple: Jessica Chastain is on the cover of the January issue of InStyle magazine

The Help star sai d: 'It completely changed the person I am. A movie, Oscars, a dress, if someone thinks I'm stupid...I realised nothing is that important.'

She also discussed another life-altering moment when she described being cast on The Tree Of Life opposite Brad Pitt, as she recalled first being told 'no one would ever cast an unknown opposite Brad Pitt'. 

Jessica told the publication: 'I knew the second Brad signed on it was a game changer for my career. Then I was just scared I was going to get fired. It wasn't until after a week of shooting that I started to relax.'

The motivation has seemingly worked as she has tallied up two Oscar nominations and a Golden Globe win since starring with the husband of Angelina Jolie in the drama.

'it was a game changer for my career': The 37-year-old actress credits working with Brad Pitt on 2011's The Tree Of Life with helping her alter her career

'it was a game changer for my career': The 37-year-old actress credits working with Brad Pitt on 2011's The Tree Of Life with helping her alter her career

 On the front of the new issue of the monthly, Jessica stuns in a clinging sleeveless purple frock featuring a cut out at the torso.

She accessorised the look with gold jewellery including bracelets and a necklace featuring a chunky gold pendant.

The Zero Dark Thirty star's fiery red locks were worn down over one shoulder as she had natural, complimentary make-up on her face.

She may be currently romantically linked to Italian fashion executive for Montcler, Gian Luca Passi de Preposulo, but she has her own personal policy on not dating actors.

Sticking to her guns: Jessica also revealed that she made the choice to not date actors early in her career, as she was pictured at a screening of A Most Violent Year in New York last month

Sticking to her guns: Jessica also revealed that she made the choice to not date actors early in her career, as she was pictured at a screening of A Most Violent Year in New York last month

She told InStyle: 'I made sure when I started that I was known for my work, not for whom I was dating.

'Acting is all about being open to another person, and to date an actor, it just confuses it, because how do you even know if it’s real?'

Jessica is currently busy promoting her upcoming film, A Most Violent Year, which is a crime drama that is set in New York during winter 1981, statistically one of the most violent years in the city's history.

In the film, Jessica plays Anna, wife of Abel (played by Oscar Isaac), a principled businessman whose growing profits threaten the New York underworld.

Her character has connections on the other side of the law, and steps up to defend the family business when her husband will not. A Most Violent Year is set to hit theaters December 31.

Upcoming: The actress can soon be seen alongside Oscar Isaac in the film A Most Violent Year, which is set for release on December 31

Upcoming: The actress can soon be seen alongside Oscar Isaac in the film A Most Violent Year, which is set for release on December 31

The comments below have been moderated in advance.

The views expressed in the contents above are those of our users and do not necessarily reflect the views of MailOnline.

We are no longer accepting comments on this article.

Who is this week's top commenter? Find out now