"I had nothing to show for myself, except for my work as an extra, and they took a chance on me.
"I think they were desperate, to tell you the truth. They were already shooting because a week later I was on set, working."
He also admitted he still cringes whenever he watches the film, because his voice on-screen is so high due to crippling nerves.
"My ass must have been clenched so tight, being the first one," he said.
Pitt's ex-wife, Angelina Jolie, recently gave a rare insight into the cause of the breakdown of their marriage.
The 45-year-old Maleficent actress addressed their 2016 split in a new interview with British Vogue, explaining it was for the "wellbeing" of her six children.
"I separated for the wellbeing of my family. I continue to focus on their healing," Jolie told the magazine.
"Some have taken advantage of my silence, and the children see lies about themselves in the media, but I remind them that they know their own truth and their own minds.
"In fact, they are six very brave, very strong young people."
It comes after Jolie made a thinly veiled swipe at Pitt in an interview with US Harper's Bazaar late last year.
In the honest interview, Jolie was asked if she would consider leaving the United States.
She replied: "I would love to live abroad and will do so as soon as my children are 18. Right now, I'm having to base where their father chooses to live."
The actress has three biological children with Pitt: Shiloh, 13, and twins Knox and Vivienne, 11. They also adopted three children: Maddox, 18, Pax, 15, and Zahara, 14.
In another subtle dig at her ex during the interview, Jolie also credited her kids with helping her "find" herself again.
"The part of us that is free, wild, open, curious can get shut down by life. By pain or by harm. My children know my true self, and they have helped me to find it again and to embrace it," she said.
"They have been through a lot. I learn from their strength. As parents, we encourage our kids to embrace all that they are and all that they know in their hearts to be right, and they look back at us and want the same for us."
The "Brangelina" split in 2016 was one of the biggest shock relationship breakdowns Hollywood has seen.
Jolie and Pitt met as co-stars on the set of Mr and Mrs Smith in 2005, began dating shortly afterwards, and eventually tied the knot in 2014.
But the couple filed for divorce in September 2016 following an incident on a plane when Pitt allegedly lost control of himself and clashed with son Maddox, then 16.
Pitt and Jolie released a joint settlement where they stated they had agreed to settle their divorce in private, and, in February 2017, Jolie spoke about the divorce for the first time, saying, "We will get through this time and hopefully be a stronger family for it".
While Pitt and Jolie were finally both declared officially single by a judge in 2019, the terms of their divorce are still being finalised.
According to US Weekly, the legal negotiations are still ongoing largely because the "sticking point is the value of Chateau Miraval" – the former couple's historic property in the south of France – and Jolie believes she should be given the entire estate because it was "her idea to purchase the property to begin with".
