Congrats to Chelsea Clinton and Marc Mezvinsky!

Former President Bill Clinton and Democratic presidential candidate Hillary Clinton's daughter announced on Twitter Saturday that she and her husband welcomed their second child.

"Marc and I are overwhelmed with gratitude and love as we celebrate the birth of our son, Aidan Clinton Mezvinsky," Chelsea, 36, wrote.

She and Marc, 38, are also parents to 1-and-a-half-year-old daughter Charlotte.

"We are overjoyed to be grandparents again with the arrival of our grandson, Aidan Clinton Mezvinsky, born on Saturday, June 18, 2016," Bill and Hillary said in a joint statement to E! News. "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 Clinton, Marc Mezvinsky

Larry Busacca/Getty Images

In January, Chelsea talked about motherhood at the American Library Association conference in Boston and said her daughter doesn't quite grasp the concept of "big sister" just yet.

"I don't think she has any idea what that means yet, but we're talking about it a lot," Chelsea said. "She says 'Baby,' and then points to herself!"

Bill Clinton, Marc Mezvinsky, Hillary Clinton, Chelsea Clinton

Justin Sullivan/Getty Images

Chelsea and Marc wed in 2010. Last December, she announced the two are expecting baby No. 2.

Throughout her pregnancy, she often helped campaign for her mother across the country and often attended rallies with her. Her most recent public appearance was last week, when she, Marc and Bill supported Hillary at a rally at the Duggal Greenhouse in Brooklyn, New York.

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