"My Son Winston Elba was born yesterday..Truly Amazing :-)," he wrote, including a black-and-white picture of the new cutie's tiny hand wrapped around his dad's fingertip.
The British actor, a 2012 Golden Globe winner for
Winston's birth has to be a moving experience for Elba, 41, who in 2010 welcomed a child he thought was his son, only to find out after taking a paternity test that he wasn't the child's father.
"The Wire" alum also has an 11-year-old daughter, Isam, from his marriage to Dormowa Sherman, a Liberian actress. Isam lives in Atlanta, and he said he doesn't get to see her very much outside of the occasional meet-up in a hotel or another temporary space, in part because he has no traditional home.
"I'm like a gypsy, man," Elba told the men's magazine. "We've had this relationship since she was 1. She's always on the road."
Last month, the "Pacific Rim" actor was reportedly in final negotiations to voice the notorious tiger Shere Khan in Disney's "Jungle Book."