Cynthia Erivo felt a "huge responsibility" to give a perfect performance of 'Defying Gravity' in 'Wicked'.

The 37-year-old star finishes the first instalment of the two-part musical adaptation with a rendition of the popular number in her role as Elphaba and had to overcome physical challenges to nail the song.

Speaking to 'Maria' star Angelina Jolie for Variety's Actors on Actors series, Cynthia said: "There was this huge responsibility, because it's such a well-known song. And people know it; people love it. I really wanted to mean it.

"The physical work of it was hard, because I'm in a harness: I'm flying and I'm singing at the same time - so many things are happening. That was new for me, to figure out how my body, my brain, my voice, would all come together to work as one. I felt really proud of being able to figure that physical, practical side of it."

Cynthia channelled her previous frustrations into the performance in order to give her performance of the song more power.

She said: "I think in order to get to a point where I could rule the words, I really thought of all the journey of getting to that moment.

"Not just in the making of this particular project, but the journey I've taken to get here: being at drama school at 20, putting myself through, finishing at 23, not getting jobs and not really being seen and not really feeling accepted - feeling very odd, very different.

"And having to figure out how to make my own way through this, because this business is hard, and this business is very hard when you're a Black girl who's singing."

The 'Defying Gravity' performance was the last sequence of the film to be shot and Cynthia was aware how eagerly the crew had been awaiting her take on the song.

She explained: "There's this other thing that's playing in my head, like, 'There are so many people on this set right now, also, who have been waiting for this moment in this film and this project, and we've all worked towards this one part.' It's how we finished; it was the last thing we shot."

Erivo has forged a close bond with her co-star Ariana Grande - who plays Galinda - during the making of 'Wicked' and revealed how the pair made a promise to protect each other when they met following the audition process.

She recalled: "We didn't audition together. We met after the roles, and we spent some time together just before we started rehearsals. And within all that, we sort of decided between each other that we were going to make sure we protected each other, that we were kind to one another, that we were going to work with each other in honesty and build a relationship from that."