The 36-year-old has vowed to play a “fully supportive” role in the child’s life despite being no longer seeing the mother-to-be, his spokeswoman said.

Law, who starred in the remake of the film Alfie, has broken the news to his ex-wife Sadie Frost and their three children.

However, it was has been reported that the woman, a New York socialite, is seeking legal advice to obtain a substantial chunk of the star’s fortune and future earnings.

A source close to the case told The Sun: “Jude is in for a seriously tough time.

“He’s accepted he’s the father and promised to do everything he can as a father. But the family in New York want it in writing.

“There is a high-powered lawyer in the girl’s family getting involved and Jude is terrified he will be cleaned out. Her family are also furious he’s had his way and disappeared back to Britain.

“The girl wants a large maintenance payment and financial costs, including a percentage of Jude’s future earnings, agreed in writing.”

The mother-to-be is seven months pregnant. According to the Daily Mirror, Law was in a relationship with her while he was working on the set of new movie Sherlock Holmes in New York, over Christmas.

A spokeswoman for the actor said: “I can confirm that following a relationship last year, Jude Law has been advised by the birth mother that he is to be the father of a child due in the autumn of this year.

We can reveal the woman having Jude Law’s lovechild is US actress and model named Samantha Burke.

Statuesque brunette Samantha, 24, above, is due to give birth to the actor’s daughter on October 6 and plans to call the baby Sophia.

Last night a source close to Jude Law said: “Samantha Burke is the mother-to-be. She and Jude had a brief relationship that ended amicably. Once the baby is born, Jude wants to visit Pensacola, in Florida, where she lives, each month. He wants to play an active part in his child’s upbringing and be supportive of both his little girl and Samantha.

“Jude is delighted he’s going to be a father again and hopes to play as much of a part in bringing her up as he has with his other children.”