Mila Kunis barely ate when she was making Black Swan

Mila told Vogue magazine: "My prep was a lot of dancing and very little eating - which I know you're not supposed to say, but it's the truth. I drank a lot of broth and danced for 12 hours a day.

"We were only supposed to have three months of prep before filming started, but we lost some financing, so that got extended to six months while Darren tried to find money.

"It sucked for Darren, but Nat and I were so happy because we had three extra months to dance."

And the intense shoot also saw Mila sustain a number of injuries, including one which left her afraid she would have to leave the production.

She said: "We would shoot those dancing scenes for hours, and I had bruises all over my ribs just from being lifted over and over again.

"I also dislocated my shoulder pretty early in the production and thought I was completely screwed, but Darren sent me to an acupuncturist and I somehow came out totally fine."

Although Darren tried to pit Natalie and Mila - who were friends before being cast - against one another during the shoot in a bid to aid their performances, the two actresses quickly realised his tactics.

The director said: "My take is that I was trying to be a sneaky director and make them argue. Mila and Natalie both realised very quickly what I was doing and made fun of me, so it quickly became a joke that we all understood. They're both very clever and were instantly privy to whatever trick I was playing. Do you guys remember it differently?"

Natalie, 44, replied: "I remember being separated from Mila and that we weren't in the same space a lot when we weren't shooting. Darren made some comment early on, like, 'Ya know, Nat, Mila's dancing so well.'

"And I was like, 'Of course she is! She's so f****** talented and I love her so much and I'm happy she's doing a great job!' "

Mila added: "Darren would tell me, 'Nat is working really, really hard. She's not even taking Saturdays and Sundays off.' Then I would text Nat and she'd be like, '...No, I'm not?'

"I think that's how we figured out what Darren was up to, but it was all in good fun."