Kate, now 37, was attending university at the time with her husband Prince William.
According to fellow student Helen McArdie, Kate "couldn't walk and she was paralytically drunk" after a big night out with friends.
Ms McArdie told the documentary Prince William at Thirty: "I remember Kate having to be carried back to her room by one of the Eton boys."
She went on to recall a similar story about Prince William.
"On another occasion, I remember William coming back - I think after celebrating the end of his exams - and falling into a bush outside of Sally's and having to be retrieved by his bodyguards.
Proving Kate has always had a cheeky side, royal writer Christopher Andersen previously revealed that Kate was given a nickname by her school friends for one antic in particular.
Just 16 at the time, the future queen once flashed her 'bottom to boys out the window.'
"She was so famous for this at the school she became known as Kate Middlebum," Mr Anderson claims.