A German-born former Catholic bishop in Norway, Georg Muller, has admitted sexually abusing a minor 20 years ago, the Norwegian Catholic Church said Wednesday.

"The Catholic Church in Norway is in shock after it was revealed that former bishop Muller of Trondheim (in southern Norway) admitted being guilty of sexual abuse of a minor and said that was why he left his post last year," the Church said in a statement.

Georg Muller, 58, who was born near Trier in Germany, stepped down as bishop of Trondheim last year, officially because he was unsuited for the work.

According to the daily Adresseavisen, which broke the story, the affair goes back more than 20 years to when Muller was a priest in Trondheim. The victim was a choir boy, who is now around 30 years old, and has been paid damages by the Church.