In a rare move that needed the pope's approval, a Lutheran convert was ordained Tuesday as a Catholic priest in Germany and is being allowed to remain married to his wife _ who has already become a nun.

Harm Klueting, 61, was ordained by Archbishop Joachim Cardinal Meisner in a private ceremony at the city's seminary, the Cologne archdiocese said.

Pope Benedict XVI gave Klueting a special permission to remain married to his wife Edeltraut Klueting, who became a Catholic Carmelite nun in 2004.

The Rev. Federico Lombardi, the Vatican's chief spokesman, said the exception is rare but there have been similar cases.

"It doesn't happen every day," he said.

Klueting and his wife were Lutherans when they married in 1977 and both served as Lutheran clerics before converting to Catholicism several years ago. They have two grown children.

The Cologne archdiocese said in a statement that the couple would not have to take the traditional vow of celibacy as long as they remain married _ a highly unusual move since celibacy is normally a key requirement for Catholic priests.

Klueting and his family could not be reached for comment, and it was not clear whether they still lived together as a couple.

Lombardi said he didn't have any specific information about the Kluetings, including what the pope said about the case.

Klueting is a professor for historical theology at the University of Cologne and teaches Catholic theology at Fribourg University in Switzerland. From now on, he also will provide services as a spiritual counselor for university students.

The archdiocese published pictures of the ordination ceremony showing Klueting with short gray hair and a beard, wearing a simple white priest vestment as he received his blessings from Meisner, who was wearing a festive yellow embroidered robe and a golden cardinal's hat.

In 1950, Pope Pius XII first allowed clergymen who had converted to Catholicism to remain married, the Cologne diocese said in its statement. However, each case has to be approved by the pope himself, the statement said, adding that in the past married priests also had been ordained in the German cities of Hamburg and Regensburg.

Last month, three former Anglican bishops were ordained as Catholic priests in London, becoming the first ex-bishops to take advantage of a new Vatican system designed to make it easier for Anglicans to embrace Roman Catholicism.

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Frances D'Emilio contributed to this report from Rome.