Answer
The unfortunate marriage between George I and his cousin Sophia Dorothea of Celle ended in divorce in 1694, primarily due to her alleged affair with Swedish soldier Count Philip Christoph von Königsmarck, who mysteriously disappeared around the same time. Their separation was instigated by George's mother, Sophia of Hanover, and led to Sophia Dorothea's confinement in Ahlden House, where she remained for the rest of her life.