On the red carpet the actress, 39, admitted that she thought her co-star Brad Pitt was gorgeous when she saw him in Thelma and Louise but someone else stole her heart: "Yes I did but I fell in love with Susan Sarandon so, you know."

Blanchett, who matched a silver Balenciaga dress with sky-high strappy gold heels, hosted the fund-raising premiere at the Sydney Theatre Company. She and husband Andrew Upton are co-artistic directors of the arts venue, which received the night's proceeds for their initiatives.

The drama, by Pitt's Se7en and Fight Club director David Fincher, stars the actor as a man born with the body of an old person who ages in reverse.

While introducing the movie, Blanchett, who plays Pitt's love interest, admitted she was nervous about appearing in a movie that uses a lot of CGI (computer-generated imagery.) She said: "When Andrew and I saw it on Friday for the first time completed I was thinking, "I'm suddenly part of a film that has so much digital technology and it's going to sort of denude what I bring to the film as an actor and it's going to make what I do obsolete but [Fincher's] been so judicious in the way he's used that it's a masterful work of direction."

The mum of three, who flew back from the States that day, shared her own magic formula for looking young: some good shut-eye. "I slept for eight hours on the plane," she said. "You know those creases you get on your eyes? That's me."

The Curious Case of Benjamin Button is out now.

Photo: Getty