Pope Benedict XVI, the earthly leader of the Catholic Church (its "visible head", according to Catholic doctrine) and sovereign of Vatican City, has announced that he will resign from his office, effective on the last day of this month. He will become the first Pope to step down willingly since Celestine V did so 1294, and the first to resign under any circumstance since Gregory XII stepped aside in 1415, to end an internal dispute within the church. When he took the office, Benedict became the first German Pope in about 900 years. In his announcement, he cited his "advanced age" as a reason for being unable to "adequately fulfill" his ministry.
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UPDATE: The Daily Mail reports lightning striking St. Peter's Basilica a few hours after the Pope's announcement.