The actress and her husband, writer/director Edoardo Ponti, welcomed a son, Leonardo Fortunato Ponti, on Monday, Dec. 20 in Geneva, Switzerland, her rep tells PEOPLE exclusively.
Leonardo joins big sister Lucia Sofia, 4½. "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.
Alexander, 37, and Ponti – who is the son of screen legend Sophia Loren – wed in Aug. 2007.
She currently stars opposite Angie Harmon on the new TNT series based upon Tess Gerritsen's popular novels.
Reporting by JULIE JORDAN