"In answer to some [journalists], I am thrilled my daughter now has a brother," the 52-year-old Notting Hill actor told his 77,000 followers. "Adore them both to an uncool degree. They have a fab mum."
"And to be crystal clear," he added, "I am the daddy."
Grant and Tinglan Hong welcomed a daughter, Tabitha, in September 2011. When his rep confirmed Tabitha's birth, the never-wed actor's relationship with Hong was described as "a fleeting affair."
"He and the mother have discussed everything and are on very friendly terms," his rep told Us Weekly at the time. The two have reportedly become more serious since the birth of their little girl.
Though 33-year-old Hong's first pregnancy wasn't planned, "I like my daughter very much," Grant revealed in a March 2012 with The Guardian. "Has she changed my life? I'm not sure. Not yet. Not massively, no. But I'm absolutely thrilled to have had her -- I really am. And I feel a better person."
The following month, Grant was singing a different tune. "Everyone was right all these years, saying, 'Hugh, why don't you have some children? It changes your life,'" he said on The Ellen DeGeneres Show. "Now that I have one, it is life changing. I recommend it. Get some!"