Angelina Jolie has opened up about working with her son Maddox Jolie-Pitt. She has said that "he was amazing" while working as an executive producer on the movie First They Killed My Father, which releases on 15 September.

Speaking on the red carpet of the Toronto International Film Festival, the Oscar-winning actress said that her 16-year-old son, who was adopted from Cambodia, "impressed" her with his dedication to the craft while working on the movie about the Cambodian genocide.

"He was amazing, he actually really impressed me, he had to earn it," the 42-year-old told ExtraTV while promoting the film at the event.

"I was able to say, you have a job, get over here, help me with this…I would say more notes, type it up, he was great."

"I can never rate my own child, but I couldn't have made it without him and I cannot say that about every producer I've worked with," she told E! News.

Brad Pitt's former wife, however, said that she waited until her eldest son was ready to make the film, which is based on Loung Ung's memoir of the same name.

She said, "When I first read it, it really affected me, but I didn't think of making a film… Loung became a friend and we became girlfriends for 16 years."

Jolie said her children — Maddox, Pax, Zahara, Shiloh and twins Knox and Vivienne — love Loung, who they call auntie. "They love her, she is family," she said.

Speaking about how the movie came about, Jolie said she and Loung penned the script years ago and they finally decided to make the movie keeping in mind Maddox's role in the movie.

"Loung and I wrote the script years ago and we talked about it being a film, but we said it really has to be about Maddox, he goes back to Cambodia often he knows what it is to be Cambodian, but to work for months and go this deep into the history, was going to be another level of understanding he had to be old enough to absorb it," she said.