Agnes von Mansfeld-Eisleben (1551–1637) was a Protestant canoness at the cloister in Gerresheim, today a district of Düsseldorf.
Her family was a cadet line of the old House of Mansfeld which, by the mid-16th century, had lost much of its affluence, but not its influence.
The Mansfeld-Eisleben line retained significant authority in its district; several of Agnes' cousins and uncles had signed the Book of Concord, and the family exercised considerable influence in Reformation affairs.
She had been raised in Eisleben, the town in which Martin Luther had been born.
The family's estates were located in Saxony, but Agnes' sister lived in the city of Cologne, married to the Freiherr (or Baron), Peter von Kriechingen.
Although a member of the Gerresheim cloister, Agnes was free during her days to go where she wished.
Reports differ on how she came to Gebhard's notice.
Some say he saw her on one of her visits to her sister in Cologne.
Others claim he noticed her during a religious procession.
Regardless, in late 1579 or early 1580, she attracted Gebhard's notice.
He sought her out, and they started a liaison.
Two of her brothers, Ernst and Hoyer Christoph, soon visited Gebhard at the archbishop's residence to discuss a marriage. "
Gebhard's Catholic belief, which was by no means based on his innermost conviction, started to waver when he had to decide whether to renounce the bishop's mitre and stay faithful to the woman he loved, or to renounce his love and remain a member of the church hierarchy."
While he considered this, rumors of his possible conversion flew throughout the Electorate.

The mere possibility of Gebhard's conversion caused consternation in the Electorate, in the Empire, and in such European states as England and France.
Gebhard considered his options, and listened to his advisers, chief among them his brother Karl, Truchsess von Waldburg (1548–1593), and Adolf, Count von Neuenahr (1545–1589).
His opponents in the Cathedral Chapter enlisted external support from the Wittelsbachs in Bavaria and from the Pope.
Diplomats shuttled from court to court through the Rhineland, bearing pleas to Gebhard to consider the outcome of a conversion, and how it would destroy the Electorate.
These diplomats assured him of support for his cause should he convert and hold the Electorate and threats to destroy him if he did convert.
The magistrates of Cologne vehemently opposed any possible conversion and the extension of parity to Protestants in the archdiocese.
His Protestant supporters told Gebhard that he could marry the woman and keep the Electorate, converting it into a dynastic duchy.
Throughout the Electorate, and on its borders, his supporters and opponents gathered their troops, armed their garrisons, stockpiled foodstuffs, and prepared for war.
On 19 December 1582, Gebhard announced his conversion, from, as he phrased it, the "darkness of the papacy to the Light" of the Word of God.
Agnes von Mansfeld-Eisleben (1551–1637) was a Protestant canoness at the cloister in Gerresheim, today a district of Düsseldorf. Her family was a cadet line of the old House of Mansfeld which, by the mid-16th century, had lost much of its affluence, but not its influence. The Mansfeld-Eisleben line retained significant authority in its district; several of Agnes' cousins and uncles had signed the Book of Concord, and the family exercised considerable influence in Reformation affairs. She had been raised in Eisleben, the town in which Martin Luther had been born. The family's estates were located in Saxony, but Agnes' sister lived in the city of Cologne, married to the Freiherr (or Baron), Peter von Kriechingen. Although a member of the Gerresheim cloister, Agnes was free during her days to go where she wished. Reports differ on how she came to Gebhard's notice. Some say he saw her on one of her visits to her sister in Cologne. Others claim he noticed her during a religious procession. Regardless, in late 1579 or early 1580, she attracted Gebhard's notice. He sought her out, and they started a liaison. Two of her brothers, Ernst and Hoyer Christoph, soon visited Gebhard at the archbishop's residence to discuss a marriage. "Gebhard's Catholic belief, which was by no means based on his innermost conviction, started to waver when he had to decide whether to renounce the bishop's mitre and stay faithful to the woman he loved, or to renounce his love and remain a member of the church hierarchy." While he considered this, rumors of his possible conversion flew throughout the Electorate.
The mere possibility of Gebhard's conversion caused consternation in the Electorate, in the Empire, and in such European states as England and France. Gebhard considered his options, and listened to his advisers, chief among them his brother Karl, Truchsess von Waldburg (1548–1593), and Adolf, Count von Neuenahr (1545–1589). His opponents in the Cathedral Chapter enlisted external support from the Wittelsbachs in Bavaria and from the Pope. Diplomats shuttled from court to court through the Rhineland, bearing pleas to Gebhard to consider the outcome of a conversion, and how it would destroy the Electorate. These diplomats assured him of support for his cause should he convert and hold the Electorate and threats to destroy him if he did convert. The magistrates of Cologne vehemently opposed any possible conversion and the extension of parity to Protestants in the archdiocese. His Protestant supporters told Gebhard that he could marry the woman and keep the Electorate, converting it into a dynastic duchy. Throughout the Electorate, and on its borders, his supporters and opponents gathered their troops, armed their garrisons, stockpiled foodstuffs, and prepared for war. On 19 December 1582, Gebhard announced his conversion, from, as he phrased it, the "darkness of the papacy to the Light" of the Word of God.
Cologne War