The Moulin Rouge actress who announced on Monday that she is expecting her first baby with her country singer husband Keith Urban is three months pregnant with her first biological child, according to her mother Janelle.
Janelle is quoted by Us Weekly magazine as saying: "I think her due date is in July."
Following the pregnancy announcement, Nicole and Keith were pictured grinning broadly while shopping together in Paddington, Australia. Asked how they were feeling about the news, Nicole said: "Very excited... thrilled!"
However, the 40-year-old star has decided to keep quiet about the sex of her unborn child, saying it is a "secret".
Nicole - who has suffered miscarriages in the past - already has two adopted children, Isabella, 15, and Connor, 12, with her ex-husband Tom Cruise. Nicole and Keith met at a black-tie ball for Australians living in Los Angeles in summer 2005.