Cate Blanchett's son's friends were ''disgusted and disappointed'' to realise she wasn't Kate Upton.

The 'Mrs. America' actress - who has Dashiel, 18, Roman, 16, Ignatius, 12, and five-year-old Edith with husband Andrew Upton - was the subject of mistaken identity because of her marital surname when her boys went to secondary school because their fellow pupils were convinced she was the swimsuit model .

She told OK! magazine: ''A fun thing happened when my boys started at their all boys' school. Their surname is Upton so I'm down on the register as Cate Upton.

''Now, there's another Kate Upton who is a rather attractive young swimsuit model and the boys at my son's school asked, 'Wait... is your mum Kate Upton?' They said, 'Yeah'.

''And so, when I showed up on the first day to pick them up, I could see the utter disappointment on those 12-year-old boys' faces. I thought, 'What have I done?'

''The disgust and disappointment was incredibly real! They were so looking forward to those play dates.''

The 51-year-old actress loves to debate the issues of the day around the dinner table with her family, and credits her kids for helping her to stay ''current''.

She said: ''I definitely think that, as one gets older, our opinions can calcify - that's why I am so grateful to my teenage children for keeping me current. Our family meals are a time for very robust and challenging discussions - and we welcome that. We push back and they push back at us. It's wonderful!''

But Cate finds it hard to ''let go'' of her kids now they are growing up.

She said: ''I think the hardest thing is having to let go. My mother always used to say it to me and I'd roll my eyes.

''She would say, 'You'll always be my child so you have to forgive me because I don't mean to treat you like a child - but that's just how I will always feel about you.'

''I now completely understand that and it drives my eldest son nuts. It's very hard to let go.''