Georgina Bloomberg, 30, the younger of Bloomberg's two daughters, gave birth to the child, named Jasper Michael Brown Quintana, at 4:34 p.m. Tuesday. The baby weighed 7 pounds, 7 ounces and a family spokesman said mother and child are "doing great" at an undisclosed New York City hospital.
The father is Georgina Bloomberg's longtime boyfriend, Ramiro Quintana. The couple are both professional equestrians, the New York Daily News reported.
The mayor, who is winding down the last few days of his 12-year tenure at City Hall, said he was excited to be a grandfather for the first time. Visiting a fire station, firefighters presented him with a No. 1 Grandpa coffee mug.
"I'm thrilled and just so proud of Georgina," the mayor said. "They are going to make really wonderful parents, and what an incredible way to start the new year."