Oscar-winning actress Julia Roberts says her life "will never be the same again" after working on the film August: Osage County.
The dark family comedy, based on Tracy Letts' Pulitzer-and Tony-winning play of the same name, made its world premiere Monday night at the Toronto International Film Festival.
Three-time Oscar winner Meryl Streep stars as Violet Weston, the pill-popping, cancer-stricken mother of three daughters, played by Roberts, Juliette Lewis and Julianne Nicholson.
The dysfunctional Oklahoma clan comes together over the course of several weeks in August after the disappearance of the patriarch, played by Sam Shepard.
The A-list cast also includes Ewan McGregor, Dermot Mulroney, Abigail Breslin and Benedict Cumberbatch.
Letts wrote the screenplay and John Wells, producer of TV series including ER and Shameless, directed. George Clooney is among the producers.
Roberts told a festival press conference Tuesday that shooting the film was the best acting experience she's ever had, but it was also the hardest she's ever worked in her life.
"Here's the thing. Here's the crux of the biscuit, if you will: We worked our asses off, because there was no other way to do it," said the box-office megastar, who cracked jokes and bantered with castmates throughout the media session.
"I've never worked so hard in my life – and I have given birth to three children. It was like a mountain to climb every single day. And the only way to climb it, we discovered, was holding hands, whether we liked it or not."
That "holding hands" experience included spending much time together almost as a family during filming in Oklahoma last year.
Co-star Chris Cooper said they "were out in the middle of nowhere" and hotel accommodations were hard to come by, so they stayed next door to each other in newly finished condos.
Streep's pad was the main hangout, where they would have potluck dinners and watch TV together. Roberts said they had to keep the momentum of the family dynamic "going really about 19 or 20 hours of the day, or else it would just leave you."
Wells said the cast members also studied each other's behaviour, particularly Streep's and Shepard's, so they would seem like they grew up in the same household.
Streep wasn't at Monday's gala premiere "due to illness," according to a statement from the festival.
She also missed Tuesday's press conference, but she was still a major focus, with cast members heaping praise on the 64-year-old acting veteran.
"Our experience was a treasure box of discovery, for me, and at the top of the heap was the person who's sleeping right now somewhere, Meryl Streep, who showed that it is about working hard," said Roberts. "I've never seen anybody work harder than she works. She doesn't sort of snap her fingers and be a genius ... she really is just the hardest-working girl in the room, and I was so grateful to see that up close."
Their collaboration wasn't exactly the way Roberts had always envisioned it would be, though.
"To work with Meryl Streep is a dream come true for anyone, to know her is an honour. She's such a beautiful person and it was intimidating, certainly, to be in these scenes with her and choking her," she said, referring to a scene involving their characters.
"Things like that are not how I pictured it going, in my mind, all these years when I thought we'd be together and we'd be having tea and speaking in fabulous accents and dressed up, looking very chic.
"And there we were and I'm sweating and have on a big butt pad, so that's not how it was in my dream."
Others also admitted they were intimidated to work with the 17-time Oscar nominee.
"The moment I got the role, I just couldn't wait for Meryl Streep to turn to me and say, 'Who are you?"' quipped Mulroney.
"I was just terrified the whole time. I was just scared every day. That was just the truth," said Breslin.
"When I read for it, I was just like, 'I'm not concerned, because I'm not going to get it.' And then I did and I was like, 'Ooo, I'm concerned."'
The cast also gushed over the play and film script.
"Tracy's got an amazing way with story and characters but especially dialogue," said Nicholson. "But he has a very specific style of writing, and if you missed a word or if you added an 'um,' it changed the whole scene."
"This is the kind of material that got me interested in acting in the first place," said Cooper.
Wells admitted it was a challenge helming a story that was already so revered.
"When it first came up it scared the hell out of me, the whole idea of being involved with it, because I consider it to be one of the great pieces of American stage literature over the last decades," he said.
"So the danger for me all along, which I shared with Tracy many times, was that I'd be the person that screwed it up."
The film is due out in November. The Toronto International Film Festival runs through Sunday.