Helen Grace was born to a surrogate and weighed in at 7 pounds, 2 ounces. She joins older brother Elliot, who was born in March 1998.
The two-time Oscar winner has a son, Raphael, and an adopted daughter, Drena, from his first marriage to Diahnne Abbott. He also has twin sons, Julian Henry and Aaron Kendrik, with his ex-girlfriend, model Toukie Smith.
De Niro, 68, and Grace, 56, first met in 1987 and married 10 years later. The couple split in 1999, but their divorce was never finalized and they renewed their vows in 2004.
De Niro can currently be seen in New Year's Eve.