London, July 30 - Hollywood actor Jude Law is about to be a father again after a brief fling with a mystery woman during Christmas.

The actor was left reeling after the mystery woman phoned him out of the blue and told him she's expecting. The mother-to-be, who has not been named, is seven months pregnant.

Jude, who already has three kids with ex-wife Sadie Frost, told her he wants to play an active role in the child's life, reported mirror.co.uk.

Their tryst is believed to have taken place over the festive season while he was working in New York on the set of new movie 'Sherlock Holmes'.

'His relationship with the girl was a passing fling, nothing serious. It was supposed to be a bit of fun for both of them. He had no idea she was pregnant until she called and told him,' said a source.