Hillary and Bill Clinton have had many notable titles: senator and governor, secretary of State and president. Now they have a new one: grandparents.The former first couple are “over the moon to be grandparents! One of the happiest moments of our life,” Hillary Clinton tweeted on Saturday.Clinton, a potential 2016 presidential candidate, also tweeted a photo of herself cradling her new granddaughter with Bill Clinton at her side.“We are blessed, grateful, and so happy to be the grandparents of a beautiful girl, Charlotte Clinton Mezvinsky, born on Friday evening, Sept. 26, 2014,” the Clintons said in a statement released Saturday. “We are thrilled to be with our daughter and her husband as they welcome their daughter into the world.”Bill Clinton has been scheduled to campaign Saturday in Colorado for Democratic Sen. Mark Udall and Gov. John Hickenlooper, but canceled because of the birth of his granddaughter. (He spoke via conference call.)The news that Chelsea Clinton and her husband, Marc Mezvinsky, were expecting their first child garnered tremendous attention in the political world — leading some to compare it to the frenzy that surrounded the arrival of Prince William and Kate Middleton’s first child, George. Chelsea Clinton revealed the news of her pregnancy at the end of a Clinton Foundation event with her mother this year at the Lower Eastside Girls Club in New York City.Hillary Clinton has stoked much of the discussion about Chelsea this year by repeatedly mentioning her excitement about becoming a grandmother. The former first lady has said she will make a decision about her plans for 2016 early next year.