The case sheds light on a little-known 60-year-old Roman Catholic church law that allows ordained clergy from other Christian faiths to become priests. "This happens seldom but it's not unusual," diocese spokesman Christoph Heckeley said, adding that it is more usual in Scandinavia.

The 61-year-old converted to Catholicism in 2004 after which he served as a deacon and taught religious history at universities in Germany and Switzerland. He currently teaches at the University of Cologne where he will also serve as a priest. Last year a married father of four was ordained as a priest in Regensburg, southern Germany.