Hannan was in Rome for meetings of the Second Session of the Second Vatican Council in November 1963 when news reached him concerning the assassination of President John F. Kennedy, which forced his immediate return to Washington. At Kennedy's state funeral Mass, Richard Cardinal Cushing, Archbishop of Boston, served as the principal celebrant. Cushing was a close friend of the family who had witnessed and blessed the marriage of Senator Kennedy and Jacqueline Bouvier in 1953, baptized two of their children, given the invocation at President Kennedy's inauguration, and officiated at the recent funeral of the President's infant son, Patrick Bouvier Kennedy.