Hugh Grant, the British actor and campaigner for tighter press regulation, has announced on Twitter that he has become a father for a second time after a newspaper obtained his new son's birth certificate.

Grant said he was "thrilled" to become a father again, reportedly with Chinese actress Tinglan Hong, but urged the press to leave his family in peace.

The 52-year-old star of "Notting Hill" was one of the most high-profile victims of phone-hacking by the former British tabloid the News of the World, and has since become a campaigner for a more responsible press.

"In answer to some journos. Am thrilled my daughter now has a brother. Adore them both to an uncool degree. They have a fab mum," Grant said in a Twitter message on Saturday evening.

He later added: "And to be crystal clear. I am the Daddy."

His announcement was in response to a story in Britain's Mail on Sunday reporting that the child, Felix Chang, was born in a west London hospital on December 29. The tabloid cited the birth certificate, issued on February 14.

Grant tweeted: "Thanks for v kind messages. Now I've confirmed (press somehow got birth certificate & were calling), hoping my family will be left in peace."

The couple's first daughter, Tabitha, was born in 2011. At the time, the actor's publicist said the couple had a "fleeting affair" and although the pregnancy was not planned, Grant "could not be happier or more supportive".