The Monster star adopted her first child, son Jackson, back in March (12) but she kept her role as a first-time mum a secret from the press for several weeks.
And Theron admits she felt so guilty coming up with lies and excuses as to why she had to stay home, she finally shared her story with Handler - and begged the comedienne to remain tight-lipped.
The actress explains, ""It actually goes to show what amazing friends I have because it didn't come out for several months. But I did find myself in weird situations.
""I met Chelsea Handler around that period and we became friends... and she said, 'Oh, you know we should go and have a drink.' And so every time she would be like, 'Let's have a drink,' I would come up with some horrible excuse. I was sick for like two months; I was like, 'Oh, my car battery is dead.' Like, whose car battery is dead?
""Then finally I was like, 'I have a baby! I can't go!' I eventually had to (tell her). Because she was like, 'What is wrong with you? If you don't want to be friends I will totally understand.' She kept it a secret.""