Cynthia Erivo and Ariana Grande "made a pact" before shooting the Wicked movies

In her new book, Simply More: A Book for Anyone Who Has Been Told They're Too Much, Cynthia explains: "Before Wicked really started rolling, Ariana and I made a pact with each other.

"We committed to protecting and caring for each other through this process. We hear often how female costars -¬ or really, any costars -¬ can sometimes let their egos get in the way until they battle each other, destroying the creative process for everyone involved. We were determined to do the opposite."

Cynthia believes she shares a "strong synergy" with her co-star, who has become a close friend in recent years.

She said: 'We were always looking out for each other. Our partnership was important. We shared a strong synergy, a commitment to authenticity, and that, combined with the natural connection we fostered both on and off set, allowed us to support each other emotionally and professionally."

Cynthia Erivo previously lavished praise on Ariana, revealing that she developed an immediate "connection" with her Wicked co-star.

The actress told Extra: "When we found out we were doing this, I asked her to come around and just chill. We organised it together and she came to my house. We sat on my floor and chatted for hours and hours and hours.

"I think in that moment, we both realised that we had something, like an immediate sort of connection."

Ariana also relished the experience of working with Cynthia on the movies.

She said: "I think the thing that's been most special about it is that, from the moment we met, our first talk, we had a really honest agreement and commitment to take care of each other and to always be honest with each other and make space for the feelings that come up along the way and just take care of each other as friends.

"That just grew and grew and grew deeper and deeper as the process went on and still is. It's just like really, really beautiful and legit. I'm so grateful."