Cate Blanchett watched her first sex scene when she was just eight years old.

Cate Blanchett

Cate Blanchett

The 46-year-old actress has admitted she first saw someone get frisky on camera when she was in third grade and her parents took her to see the risqué 1976 film 'Silver Streak.'

Speaking to W magazine, she said: "I remember the first time I saw a sex scene. My parents took me, I think I was third grade. It had Gene Wilder in it, it was 'Silver Streak'.

"There was a sequence in it but he's on a runaway train, so you think it's going to be funny and we can take the kids to that, but he was with this woman on a runaway train, running from the law, and he'd hurt himself.

"She started to kiss him. And he said, 'Well actually it hurts here and here' and I thought, 'Where is this going?' And she started to unbutton his shirt.

"I could feel my mother's buttocks clenching beside me. And I thought, 'Ooo I want some of that.'"

Meanwhile, the 'Carol' star - who has three biological sons, Dashiell, 14, Roman, 11, and Ignatius, eight, and adopted baby daughter Edith with her husband Andrew Upton - was forced to defend herself last month when rumours about her sexuality began to surface after she was quoted saying she had enjoyed relationships with women "many times".

She said recently: "It really is of no relevance what my sexual persuasion is."