WASHINGTON - Hillary and Bill Clinton welcomed the birth Saturday of their second grandchild, gushing that they are "over the moon" about the arrival to the world of baby Aidan Mezvinsky. "We are overjoyed to be grandparents again with the arrival of our grandson, Aidan Clinton Mezvinsky, born on Saturday, June 18, 2016," the proud grandparents wrote in a statement.

"We are all over the moon as Chelsea and Marc welcome Charlotte's little brother to the world and grateful for our many blessings. Chelsea and Aidan are both doing well and enjoying this very special time together." Chelsea a short time earlier had announced via Twitter that she and husband Marc Mezvinsky had become parents to a baby boy. "Marc and I are overwhelmed with gratitude and love as we celebrate the birth of our son, Aidan Clinton Mezvinsky," the former first daughter tweeted.

Their little girl, Charlotte Clinton Mezvinsky, was born in 2014.

Hillary Clinton, the presumptive Democratic nominee for the November presidential election, has boasted that being a grandmother is one of the achievements of which she is most proud.

Daughter Chelsea is the vice chair of the Clinton Foundation, a non-profit organisation founded by her Bill Clinton to improve health around the world. Her husband is an investment banker.