The Four Weddings and a Funeral star's on/off girlfriend Tinglan Hong has given birth to a baby boy.
Grant announced the happy news on Twitter on Saturday.
"In answer to some journos, am thrilled my daughter now has a brother," he said.
"Adore them both to an uncool degree. They have a fab mum."
He later added, "And to be crystal clear. I am the Daddy."
The 52-year-old and Hong first became parents in 2011.
Details of the newborn's name and his exact date of birth have not been released.