Chelsea Clinton is engaged to her longtime boyfriend Marc Mezvinsky, a spokesman for former President Bill Clinton confirmed to ABC News. Clinton, 29, is the only child of the former president and current Secretary of State Hillary Clinton. She and Mezvinsky -- the son of former Rep. Ed Mezvinsky and former Rep. Marjorie Margolies-Mezvinksy -- became friends in Washington, D.C., and closer friends when they both attended Stanford University.