America's former first daughter Chelsea Clinton said Thursday that she is to be a mother for the first time, giving her delighted parents Bill and Hillary a long-awaited grandchild. Chelsea, 34, made the announcement at a public event with her mother in New York organized by a Clinton Foundation initiative to advance the cause of women and girls around the world. "Marc and I are very excited that we have our first child arriving later this year," Chelsea told the audience at the Lower Eastside Girls Club, to whoops of delight from the crowd. "Excited to add a new line to my Twitter bio... grandfather-to-be! @HillaryClinton and I are so happy for Chelsea and Marc!," tweeted Bill.