The Oscar-winning actress welcomed her third son – who weighed a healthy 7lbs 9oz – with husband Andrew Upton in a hospital in Sydney, Australia.
Popular on LondonNet
A spokesman for the 38-year-old actress said: “All are well and very happy.”
Cate and 41-year-old playwright Andrew already have two children, six-year-old Dashiell John and three-year-old Roman Robert.
While Cate’s official due date is unknown, she revealed last week she was overdue.
Cate and Andrew – who have been married for 10 years – are based in Australia, where they also work as co-directors of the Sydney Theatre Company.
The actress recently revealed becoming a mother has made her a better person and improved her life more than she could ever have imagined.
She said: “you realise how much love you’re actually capable of. It’s like more doors open in your personality that you didn’t even realise were there.
“It’s a trip, being a parent, a privilege – even though it means you get a lot less sleep!”
