By Barbara Goldberg

NEW YORK (Reuters) - Chelsea Clinton, daughter of U.S. Democratic presidential candidate Hillary Clinton and former President Bill Clinton, announced on Saturday the birth of her second child with husband Marc Mezvinsky.

Aidan Clinton Mezvinsky was born on Saturday to Clinton and her investment banker husband, according to a statement released by the proud grandparents. His older sister, Charlotte Clinton Mezvinsky, was born on Sept. 27, 2014.

"We are all over the moon as Chelsea and Marc welcome Charlotte’s little brother to the world and grateful for our many blessings," Hillary and Bill Clinton said in the statement.

"Chelsea and Aidan are both doing well and enjoying this very special time together," they said.

Chelsea Clinton, 36, took to Twitter late Saturday morning to announce Aidan's birth. Her spokeswoman said the she delivered at Lenox Hill Hospital on Manhattan's Upper East Side.

"Marc and I are overwhelmed with gratitude and love as we celebrate the birth of our son, Aidan Clinton Mezvinsky," Clinton said on Twitter.

Chelsea Clinton is the only child of the former president and the former U.S. secretary of State, who is running for president in November. Chelsea Clinton lives in New York City and is the vice chair of the Clinton Foundation, a charity that focuses on global health issues among other causes.

Clinton and Mezvinsky were married in August 2010. He is the son of two former Democratic members of Congress, former Representative Marjorie Margolies-Mezvinsky of Pennsylvania and former Representative Ed Mezvinsky of Iowa.

Clinton revealed in December that she was due to give birth to a second child, posting on Twitter, "Next summer, Charlotte is going to be a big sister!"

Details about the baby boy's delivery, such as time of birth and weight, were not immediately available, according to Chelsea Clinton's spokeswoman Erika Gudmundson.

In March, 2016 Republican presidential candidate Donald Trump welcomed a grandson of his own when his daughter Ivanka and her husband Jared Kushner announced the birth of their third child, Theodore James Kushner. The baby is Trump's eighth grandchild.

(Reporting by Barbara Goldberg; Editing by Cynthia Osterman)