"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 tweeted Saturday morning. "And to be crystal clear. I am the Daddy."
E! Online said Hong and Grant had their first child, Tabitha, in September of 2011.
In an interview with Ellen DeGeneres last year, Grant said he enjoys parenthood.
"Everyone was right all these years, saying, 'Hugh, why don't you have some children? It changes your life,'" Grant said. "Now that I have a child, it is life changing. I recommend it. Get some!"
2014: The Year in Music [PHOTOS]