Charlize Theron and Tom Hardy put up ''walls to protect themselves'' on the set of 'Mad Max: Fury Road'.

The duo had a feud behind-the-scenes of the 2015 movie and now they are opening up about just why they struggled so much with one another.

She said: ''In retrospect, I didn't have enough empathy to really, truly understand what he must have felt like to step into Mel Gibson's shoes. That is frightening! I think because of my own fear, we were putting up walls to protect ourselves instead of saying to each other, 'This is scary for you, and it's scary for me, too. Let's be nice to each other.' In a weird way, we were functioning like our characters: Everything was about survival.''

And Tom admits the pressure on both of them was ''overwhelming'' at times and it made it difficult for both of them to perform on set.

He added to The New York Times: ''I think in hindsight, I was in over my head in many ways. The pressure on both of us was overwhelming at times. What she needed was a better, perhaps more experienced, partner in me. That's something that can't be faked. I'd like to think that now that I'm older and uglier, I could rise to that occasion. Because of how much detail we were having to process and how little control one had in each new situation, and how fast the takes were - tiny snippets of story moments were needed to make the final cut work - we moved fast, and it was at times overwhelming. One had to trust that the bigger picture was being held together.''