The Catholic Bishop of Arundel and Brighton has resigned, saying he has brought "shame" on the diocese.
The Rt Rev Kieran Conry, whose diocese covers Sussex and Surrey, said he had been "unfaithful" to his promises as a Catholic priest.
He said his actions "were not illegal and did not involve minors".
He apologised to those "hurt by my actions and then to all of those inside and outside the diocese who will be shocked, hurt and saddened".
He said his resignation would take immediate effect, and he would now take time to consider his future.
Bishop Kieran's statement did not specify in what way he had been "unfaithful" to his promises but it will be read in all Catholic churches over the weekend.
His statement ended: "I am sorry for the shame that I have brought on the diocese and the Church and I ask for your prayers and forgiveness."
Cardinal Vincent Nichols, head of the Catholic Church in England and Wales, said: "This is a sad and painful moment.
"It makes clear that we are always a Church of sinners called to repentance and conversion and in need of God's mercy.
"All involved in this situation are much in my prayers today."