Leonardo Fortunato Ponti was born Monday, Dec. 20 in Geneva, Switzerland.
“We are so thrilled to welcome our little Leonardo. He’s a wonderful gift and we are all in love – especially the grandmas!” the couple said in a statement.
The 37-year-old actress married Ponti, the son of screen legend Sophia Loren, in August 2007. The couple also have a daughter, Lucia, age 4.
Alexander starred in the first two seasons of “NCIS,” and currently co-stars with Angie Harmon on the hit TNT crime drama, “Rizzoli & Isles.”