The lecture was part of a conference called 'The Flight Of The Hummingbird' - 'The Future Of Children In The Mind And Society Of The World.'
However, at the last moment she pulled out of the talk due to "personal reasons".
Italian papers have claimed that the 32-year-old actress did so because she discovered that she is expecting her second child with Pitt.
Letizia Manjani, a spokewoman for the centre has revealed that she couldn't keep the news a secret - despite her being under a gagging order.
"Angelina cancelled last week. Due to her privacy I can't confirm her pregnancy, but I can say that the Italian newspapers are correct in their reports," The Sun quoted Manjani, as saying.