Reese Witherspoon as claimed she was once in an abusive relationship, which "damaged" her "self-esteem".
The 41-year-old actress - who is now married to Jim Toth, with whom she has five-year-old son Tennessee - has admitted that leaving the past relationship, in which she was allegedly "psychologically and verbally" abused, had a "profound" affect on her.
When asked what the most difficult task in her life has been, Reese - who also has 18-year-old daughter Ava and 14-year-old son Deacon with her ex-husband Ryan Phillippe - said: "For me, probably leaving an abusive relationship. A line got drawn in the sand and it got crossed, and my brain just switched and I knew it was going to be very difficult but I just couldn't go any further. But it was profound and I was young."
And Reese insists the alleged experience has helped shape who she is today, as leaving the relationship "changed" her "on a cellular level".
During an interview with her 'A Wrinkle In Time' co-stars Oprah Winfrey and Mindy Kahling for Oprah's O Magazine, she said: "I could never be the person I am today. It changed who I was on a cellular level, the fact that I stood up for myself. None of those leaving those situations ... it's wrought with self-doubt, particularly if someone damages your self-esteem.
"People say to me that knew me then, 'You're a completely different person.' I didn't have self-esteem. I'm a different person now and it's part of why I can stand up and say, 'yes, I'm ambitious' - because someone tried to take that from me before."
Oprah, 64, also shared her own experience with abusive relationships, in which she stated she had been a victim of verbal abuse whilst in her 20s.
She said: "I lived in that superior, better-than-thou space where, 'As long as he doesn't hit me, he can say anything, he can do anything, but as long as he doesn't hit me.'"
The star - who is now in a longterm relationship with Stedman Graham - then recalled that it wasn't until her hand was slammed into a door that she realised she "had become that woman who would allow myself to be psychologically, verbally assaulted."