Jude Law is set to become a father for the fourth time after a brief relationship with an unknown woman, it was disclosed today.

Parental role: Jude Law is no longer involved with the woman pregnant with his child

Law, 36, is said to be prepared to play a “fully supportive” role in the child's life despite no longer being involved with the expectant mother.

The unnamed woman is believed to be about seven months pregnant following a brief affair with Law over the Christmas period.

Ex-wife: the actor with Sadie Frost and one of their three children

The actor was working in New York on the set of the film Sherlock Holmes at the time. He is said to have been told of the woman's pregnancy only recently. He is believed to have broken the news to his ex-wife, Sadie Frost, with whom he has three children, on Tuesday.

A spokesman for Law said today: “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.

“He is no longer in a relationship with her but he intends to be a fully supportive part of the child's life.

“This is an entirely private matter and no further statements will be made.”

Law, currently receiving rave reviews for his performances as Hamlet in the West End, is expected to return to New York soon when the Michael Grandage-directed production transfers to Broadway.

After his seven-year marriage to Ms Frost, 44, ended in 2003, Law began a relationship with actress Sienna Miller. That ended when it was revealed he had an affair with his children's nanny, Daisy Wright.

Since then he has been seen in the company of a number of actresses and models, including Cameron Diaz and Rod Stewart's daughter Kimberly. A source close to the actor was reported as saying today: “His relationship with the girl was a passing fling, nothing serious. Jude is a family man and he would not choose for a child to be born under these circumstances. But he wants to behave honourably.

“Jude's main concern is his family so he visited Sadie at home in London this week to tell them. There are, of course, financial implications. But Jude is adamant these will not affect his relationship with his family.

“He will not shy away from his parental duties and wants to be involved as much as possible.”