Although Kidman said keeping quiet about Faith Margaret was one of the toughest things she's ever had to do.
Speaking to E! presenter Giuliana Rancic on the red carpet at yesterday's Screen Actors Guild Awards, Nicole said: 'I wanted to be able to tell everybody because I was so excited about her.
'We just decided this was our thing together, it kind of just perpetuated itself.'
The 43-year-old added: '[And] it protects her.
'And it protects everyone in the situation.'
The actress and husband Keith Urban revealed earlier this month that they had welcomed the baby to the family after she was born via a surrogate mother.