Chelsea Clinton announced that she and her husband, Marc Mezvinsky, are expecting their second child.

Clinton made the announcement Monday in a Twitter post that shows a photo of the couple’s 15-month-old daughter, Charlotte, reading a book titled “Big Sisters are the Best.”

Clinton’s mother, Democratic presidential candidate and former Secretary of State Hillary Rodham Clinton, responded on Twitter moments later saying she and her husband, former President Bill Clinton, are “so excited to meet our second grandchild.”