Pope Benedict XVI announced Monday morning that he will resign, effective Feb. 28, according to the Associated Press.

CNN reported that a spokesman for the pope did not give a reason for the decision, announced during a meeting of Vatican cardinals, but according to the AP, the 85-year-old pontiff cited his "advanced age and diminishing strength."

Cardinal Francis George was surprised by the announcement, according to the Chicago Tribune . George returned to Chicago yesterday from a visit at the Vatican, where he attended committee meetings. The Cardinal issued an official statement Monday morning, referring to the pope's resignation as a brave decision.

Pope Benedict XVI has, in all circumstances, placed the will of God for the good of the Church before every other consideration.  That same resoluteness of purpose speaks in his statement announcing his resignation from the Chair of Peter.

He has taught with clarity and charity what God has revealed to the world in Christ; he has handed on the apostolic faith; he has loved all of God’s people with all his heart.  He has now shown great courage in deciding, after prayer and soul-searching, to resign his office at the end of this month.

With the gratitude of sons and daughters in our hearts, we ask the Lord to bless him and give him strength, as we begin to pray now for the one who will succeed him as Bishop of Rome, Successor of Peter and Vicar of Christ. —Francis Cardinal George

The decision makes Benedict the first pope to resign in nearly 600 years, according to the AP report.

Born Joseph Ratzinger, Pope Benedict XVI was chosen in 2005 to succeed the late Pope John Paul II.

The Vatican could hold a conclave to elect a new pope by mid-March, according to the AP.